9951 Roll src/third_party/dart 63120303a7…a089199b93 (cla: yes)

9952 ios: Fixed the callback for the first frame so that it isn’t predicated on having a splash screen. (cla: yes)

9953 [macos] Add reply to binary messenger (cla: yes)

9954 Add working Robolectric tests (cla: yes)

9958 Clean up cirrus.yml file a little (cla: yes)

9959 Update Dart engine tests to check for assertion failures only when running in debug mode (cla: yes)

9961 Fix return type of assert function in gradient_test (cla: yes)

9977 Fix flutter/flutter #34791 (cla: yes, platform-android)