27291 Roll Dart SDK from a8c4933bf92e to 83a559e0a9bd (2 revisions) (cla: yes, waiting for tree to go green)

27293 Roll Skia from b161a77d0321 to 4b6e2f0d8818 (4 revisions) (cla: yes, waiting for tree to go green)

27295 Fix the firebase scenario app run and assert that it does good things (platform-android, cla: yes, waiting for tree to go green, needs tests)

27298 Roll Dart SDK from 83a559e0a9bd to ab8bac9fd542 (1 revision) (cla: yes, waiting for tree to go green)