21471 Roll Skia from 427d8ebf308c to e96cdd18ac5f (6 revisions) (cla: yes, waiting for tree to go green)

21472 Roll Dart SDK from 58248a54dd58 to 281f1e388107 (1 revision) (cla: yes, waiting for tree to go green)

21473 Clear the Minikin layout cache during engine destruction (cla: yes)

21474 Replace kLegacyFontHost_InitType with kUnknown_SkPixelGeometry. (cla: yes)

21475 Roll Dart SDK from 281f1e388107 to 4c0245356649 (1 revision) (cla: yes, waiting for tree to go green)