28467  Factor out a task synchronization help function for unit tests (cla: yes, waiting for tree to go green)

28468 Roll Skia from 360db877be35 to f65cd9be7330 (1 revision) (cla: yes, waiting for tree to go green)

28470 Roll Fuchsia Mac SDK from lOgxSvrjd… to 7OyGTsKNy… (cla: yes, waiting for tree to go green)

28471 Roll Fuchsia Linux SDK from GpAkjCJKU… to eYuGUghZ1… (cla: yes, waiting for tree to go green)

28472 Roll Fuchsia Mac SDK from 7OyGTsKNy… to bmShnqcSD… (cla: yes, waiting for tree to go green)