The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards #171790

re-land attempt for #172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

…173114)" (#173145)

<!-- start_original_pr_link -->
Reverts: #173114
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: jtmcdole
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: there is still another problem with the merge
queue causing the content hash to be different:

git revision: e13dd53
actual hash: 4b6f7b0f9849efaa59f515c8e95f3f27a6eb2ffb
hash in the queue? 9e5b2eef4ba79b15b4f80dbba812d199d262366f



<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: jtmcdole
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {matanlurey, chingjun}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards #171790

re-land attempt for #172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

…mpt) (#173169)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards #171790

re-land attempt for #173114 (try 2)
re-land attempt for #172792 (original)

The first commit in this PR is the previously LGTM'd changes for the
above; with tests.

The second commit is the critical change to make this work in post
submits (fixes #173143). It turns out that while LUCI reports the GitHub
private branches; our recipes directly checkout the git sha. This
matters because the content scripts couldn't determine the branch name
and the rev-parse was just HEAD. This lead the scripts down the
merge-base logic, which returns the previous commit.

A test was added specifically for this.

Alternatively to this change, we could have checked for LUCI_CONTEXT
being present in the environment. This is checked by Flutter tools in
some cases, but not by any other scripts in `bin/internal`. The downside
to checking HEAD: if you have a local branch with engine changes and you
move back a revision - `dart`/`flutter` invocations will generate the
hash for your local changes and fail.

…mpt) (flutter#173169)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#173114 (try 2)
re-land attempt for flutter#172792 (original)

The first commit in this PR is the previously LGTM'd changes for the
above; with tests.

The second commit is the critical change to make this work in post
submits (fixes flutter#173143). It turns out that while LUCI reports the GitHub
private branches; our recipes directly checkout the git sha. This
matters because the content scripts couldn't determine the branch name
and the rev-parse was just HEAD. This lead the scripts down the
merge-base logic, which returns the previous commit.

A test was added specifically for this.

Alternatively to this change, we could have checked for LUCI_CONTEXT
being present in the environment. This is checked by Flutter tools in
some cases, but not by any other scripts in `bin/internal`. The downside
to checking HEAD: if you have a local branch with engine changes and you
move back a revision - `dart`/`flutter` invocations will generate the
hash for your local changes and fail.

…3114)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

…lutter#173114)" (flutter#173145)

<!-- start_original_pr_link -->
Reverts: flutter#173114
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: jtmcdole
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: there is still another problem with the merge
queue causing the content hash to be different:

git revision: e13dd53
actual hash: 4b6f7b0f9849efaa59f515c8e95f3f27a6eb2ffb
hash in the queue? 9e5b2eef4ba79b15b4f80dbba812d199d262366f



<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: jtmcdole
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {matanlurey, chingjun}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

…mpt) (flutter#173169)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#173114 (try 2)
re-land attempt for flutter#172792 (original)

The first commit in this PR is the previously LGTM'd changes for the
above; with tests.

The second commit is the critical change to make this work in post
submits (fixes flutter#173143). It turns out that while LUCI reports the GitHub
private branches; our recipes directly checkout the git sha. This
matters because the content scripts couldn't determine the branch name
and the rev-parse was just HEAD. This lead the scripts down the
merge-base logic, which returns the previous commit.

A test was added specifically for this.

Alternatively to this change, we could have checked for LUCI_CONTEXT
being present in the environment. This is checked by Flutter tools in
some cases, but not by any other scripts in `bin/internal`. The downside
to checking HEAD: if you have a local branch with engine changes and you
move back a revision - `dart`/`flutter` invocations will generate the
hash for your local changes and fail.

…2792)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards  flutter#171790

…lutter#172792)" (flutter#172805)

<!-- start_original_pr_link -->
Reverts: flutter#172792
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: jtmcdole
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: almost, but not quite right. android builders
generate the wrong hash because they are on custom branches.
<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: jtmcdole
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {bdero, matanlurey}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards  flutter#171790 

<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

…3114)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

…lutter#173114)" (flutter#173145)

<!-- start_original_pr_link -->
Reverts: flutter#173114
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: jtmcdole
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: there is still another problem with the merge
queue causing the content hash to be different:

git revision: e13dd53
actual hash: 4b6f7b0f9849efaa59f515c8e95f3f27a6eb2ffb
hash in the queue? 9e5b2eef4ba79b15b4f80dbba812d199d262366f



<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: jtmcdole
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {matanlurey, chingjun}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

…mpt) (flutter#173169)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#173114 (try 2)
re-land attempt for flutter#172792 (original)

The first commit in this PR is the previously LGTM'd changes for the
above; with tests.

The second commit is the critical change to make this work in post
submits (fixes flutter#173143). It turns out that while LUCI reports the GitHub
private branches; our recipes directly checkout the git sha. This
matters because the content scripts couldn't determine the branch name
and the rev-parse was just HEAD. This lead the scripts down the
merge-base logic, which returns the previous commit.

A test was added specifically for this.

Alternatively to this change, we could have checked for LUCI_CONTEXT
being present in the environment. This is checked by Flutter tools in
some cases, but not by any other scripts in `bin/internal`. The downside
to checking HEAD: if you have a local branch with engine changes and you
move back a revision - `dart`/`flutter` invocations will generate the
hash for your local changes and fail.

…2792)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards  flutter#171790

…lutter#172792)" (flutter#172805)

<!-- start_original_pr_link -->
Reverts: flutter#172792
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: jtmcdole
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: almost, but not quite right. android builders
generate the wrong hash because they are on custom branches.
<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: jtmcdole
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {bdero, matanlurey}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards  flutter#171790 

<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

…3114)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

…lutter#173114)" (flutter#173145)

<!-- start_original_pr_link -->
Reverts: flutter#173114
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: jtmcdole
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: there is still another problem with the merge
queue causing the content hash to be different:

git revision: e13dd53
actual hash: 4b6f7b0f9849efaa59f515c8e95f3f27a6eb2ffb
hash in the queue? 9e5b2eef4ba79b15b4f80dbba812d199d262366f



<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: jtmcdole
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {matanlurey, chingjun}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

…mpt) (flutter#173169)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#173114 (try 2)
re-land attempt for flutter#172792 (original)

The first commit in this PR is the previously LGTM'd changes for the
above; with tests.

The second commit is the critical change to make this work in post
submits (fixes flutter#173143). It turns out that while LUCI reports the GitHub
private branches; our recipes directly checkout the git sha. This
matters because the content scripts couldn't determine the branch name
and the rev-parse was just HEAD. This lead the scripts down the
merge-base logic, which returns the previous commit.

A test was added specifically for this.

Alternatively to this change, we could have checked for LUCI_CONTEXT
being present in the environment. This is checked by Flutter tools in
some cases, but not by any other scripts in `bin/internal`. The downside
to checking HEAD: if you have a local branch with engine changes and you
move back a revision - `dart`/`flutter` invocations will generate the
hash for your local changes and fail.

…2792)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards  flutter#171790

…lutter#172792)" (flutter#172805)

<!-- start_original_pr_link -->
Reverts: flutter#172792
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: jtmcdole
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: almost, but not quite right. android builders
generate the wrong hash because they are on custom branches.
<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: jtmcdole
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {bdero, matanlurey}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards  flutter#171790 

<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

…3114)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

…lutter#173114)" (flutter#173145)

<!-- start_original_pr_link -->
Reverts: flutter#173114
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: jtmcdole
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: there is still another problem with the merge
queue causing the content hash to be different:

git revision: e13dd53
actual hash: 4b6f7b0f9849efaa59f515c8e95f3f27a6eb2ffb
hash in the queue? 9e5b2eef4ba79b15b4f80dbba812d199d262366f



<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: jtmcdole
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {matanlurey, chingjun}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

…mpt) (flutter#173169)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#173114 (try 2)
re-land attempt for flutter#172792 (original)

The first commit in this PR is the previously LGTM'd changes for the
above; with tests.

The second commit is the critical change to make this work in post
submits (fixes flutter#173143). It turns out that while LUCI reports the GitHub
private branches; our recipes directly checkout the git sha. This
matters because the content scripts couldn't determine the branch name
and the rev-parse was just HEAD. This lead the scripts down the
merge-base logic, which returns the previous commit.

A test was added specifically for this.

Alternatively to this change, we could have checked for LUCI_CONTEXT
being present in the environment. This is checked by Flutter tools in
some cases, but not by any other scripts in `bin/internal`. The downside
to checking HEAD: if you have a local branch with engine changes and you
move back a revision - `dart`/`flutter` invocations will generate the
hash for your local changes and fail.

…utter/flutter#172792)

…2792)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards  flutter#171790

…lutter#172792)" (flutter#172805)

<!-- start_original_pr_link -->
Reverts: flutter#172792
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: jtmcdole
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: almost, but not quite right. android builders
generate the wrong hash because they are on custom branches.
<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: jtmcdole
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {bdero, matanlurey}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards  flutter#171790 

<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

…3114)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

…lutter#173114)" (flutter#173145)

<!-- start_original_pr_link -->
Reverts: flutter#173114
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: jtmcdole
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: there is still another problem with the merge
queue causing the content hash to be different:

git revision: e13dd53
actual hash: 4b6f7b0f9849efaa59f515c8e95f3f27a6eb2ffb
hash in the queue? 9e5b2eef4ba79b15b4f80dbba812d199d262366f



<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: jtmcdole
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {matanlurey, chingjun}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#172792  with the following changes:

1. content_aware_hash.(ps1|sh) now consider multiple branches to choose
between HEAD and merge-base.
2. content_aware_hash_test.dart updated for these new requirements 
3. content_aware_hash_test.dart allows for forcing powershell on mac for
testing
4. updated docs/tool/Engine-artifacts.md documentation.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

…mpt) (flutter#173169)

The content hash doesn't exist for local engine changes, except for on
CI. If we detect we're on a branch with committed or uncommitted changes
to engine files; use "master".

towards flutter#171790

re-land attempt for flutter#173114 (try 2)
re-land attempt for flutter#172792 (original)

The first commit in this PR is the previously LGTM'd changes for the
above; with tests.

The second commit is the critical change to make this work in post
submits (fixes flutter#173143). It turns out that while LUCI reports the GitHub
private branches; our recipes directly checkout the git sha. This
matters because the content scripts couldn't determine the branch name
and the rev-parse was just HEAD. This lead the scripts down the
merge-base logic, which returns the previous commit.

A test was added specifically for this.

Alternatively to this change, we could have checked for LUCI_CONTEXT
being present in the environment. This is checked by Flutter tools in
some cases, but not by any other scripts in `bin/internal`. The downside
to checking HEAD: if you have a local branch with engine changes and you
move back a revision - `dart`/`flutter` invocations will generate the
hash for your local changes and fail.