27811 Reland using preDraw for the Android embedding (platform-android, cla: yes, waiting for tree to go green)

27812 Roll Dart SDK from 6e821afc0cb4 to a325ab04ed38 (1 revision) (cla: yes, waiting for tree to go green)

27813 Roll Skia from d31b15da6e33 to 8adb6255053f (1 revision) (cla: yes, waiting for tree to go green)

27814 Roll Skia from 8adb6255053f to 14d87226b3ad (5 revisions) (cla: yes, waiting for tree to go green)

27815 [web] Code cleanup (cla: yes, platform-web)