Description

This PR moves Gallery web benchmarks out of Flutter proper and separates the dependencies for flutter/flutter and flutter/gallery, allowing the two repos to freely update dependencies in the future, while preserving the important benchmarks which give us tons of useful signals, not just performance, but stability also.

These two PRs (see References section below) behave in the following way:

1. flutter side — Creates a new package web_benchmarks inside packages, and updates existing web benchmarks to use this package. Also rewrites Gallery benchmarks in flutter/flutter to stop using pubspec.yaml dependencies, and start pulling flutter/gallery at runtime.
2. gallery side — Adds Gallery benchmarks (browser side) to the flutter/gallery, using the newly created web_benchmarks package.

The two PRs must be landed in this order.

Currently, some dependencies / git references are pointing to my own branches. They will be moved to official branches once the corresponding prerequisites are landed.

References

Flutter side — #66911
Gallery side — flutter/gallery#333

Related Issues

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Tests

No tests are added here.
Tests are added for the web_benchmarks package.

Checklist

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
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Breaking Change

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• No, no existing tests failed, so this is not a breaking change.
• Yes, this is a breaking change. If not, delete the remainder of this section.
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