21244 Roll Skia from 51a7f9559ad4 to 12d06a38427d (3 revisions) (cla: yes, waiting for tree to go green)

21245 Roll Dart SDK from 99970d646dc9 to fcaedc6d9587 (3 revisions) (cla: yes, waiting for tree to go green)

21246 Roll Fuchsia Linux SDK from 91U3isvKn… to Qi0ptKLxN… (cla: yes, waiting for tree to go green)

21247 [web] Remove commented import (cla: yes, platform-web)

21248 avoid hard coding OS (cla: yes, waiting for tree to go green)