27680 Log all Skia trace events if the –trace-skia flag is passed (cla: yes, waiting for tree to go green)

27681 Roll Dart SDK from e1e2ab3a7acb to 344338e1b540 (1 revision) (cla: yes, waiting for tree to go green)

27682 Roll Skia from 64565aed5151 to feb459a1fb51 (17 revisions) (cla: yes, waiting for tree to go green)

27683 fix a number of conditions for computing bounds from saveLayers (cla: yes, waiting for tree to go green)

27684 Specify the output paths of the scenario app lint task (cla: yes, waiting for tree to go green)