flutter run doesn't pick up code changes in dependent packages with gradle #8315

Steps to Reproduce (on Linux)

1. mkdir mylib
2. mkdir mylib/lib
3. echo "name: mylib" > mylib/pubspec.yaml
4. echo "const int generation = 1;" >> mylib/lib/bar.dart
5. flutter create foobar
6. cd foobar
7. Add the following to the "dependencies" section of your pubspec.yaml:

  mylib:
    path: ../mylib

8. Add an import "package:mylib/bar.dart"; to lib/main.dart
9. Change 'Button tapped $_counter time${ _counter == 1 ? '' : 's' }.', to '$generation',
10. flutter run

Notice that you see the number 1 in the middle of the screen.

11. Edit ../mylib/lib/bar.dart to change generation from 1 to 2.
12. flutter run

Notice that you still see the number 1 in the middle of the screen instead of 2, which is what the code currently does.

Discussion

As part of the build, we output ./android/app/build/intermediates/flutter/debug/snapshot_blob.bin.d, which lists the Dart files that were read during the build. If any of those files change, we need to recreate the snapshot to see the code change. It appears the gradle build is ignoring this file and only considering code changes inside the gradle project itself.

/cc @jakobr-google @eseidelGoogle @goderbauer