In Dart 2.0, int type is going to be a fixed-size 64-bit integer. See https://github.com/dart-lang/sdk/blob/master/docs/language/informal/int64.md for details.

Flutter message codecs support sending/receiving large integers, so we might consider revising this API to better fit fixed-size integers (either drop support for large integers, or use the new Dart BigInt class).

This change updates message codecs test to stop using large integer literals (which are illegal in Dart 2.0)

/cc @mravn-google @cbracken @floitschG