15678 Support animated images in the CanvasKit backend (cla: yes)

15681 [web] update dart:js and dart:js_util to new upstream locations (cla: yes)

15682 Roll src/third_party/skia 7655168e6865..7edb0eb8a458 (16 commits) (autoroller: commit, cla: yes)

15683 Roll src/third_party/dart 862d5012ae9c..515d4bd7adb1 (18 commits) (autoroller: commit, cla: yes)

15686 Roll src/third_party/skia 7edb0eb8a458..2900040bc4a0 (3 commits) (autoroller: commit, cla: yes)