28045 Fix some warnings seen after the migration to JDK 11 (platform-android, cla: yes, waiting for tree to go green, needs tests)

28048 Roll Skia from ec07af1279ec to 1fc789943486 (8 revisions) (cla: yes, waiting for tree to go green)

28049 Roll Dart SDK from 8e3be460559f to 7b142a990f2b (2 revisions) (cla: yes, waiting for tree to go green)

28051 Roll Skia from 1fc789943486 to c01225114a00 (1 revision) (cla: yes, waiting for tree to go green)