18852 null-annotate remaining engine code (cla: yes)

18853 Roll Skia from 9f7485b4bbeb to aa10dfeec96a (8 revisions) (cla: yes, waiting for tree to go green)

18854 Roll Dart SDK from 249cb9c974e1 to 403955cf347f (9 revisions) (cla: yes, waiting for tree to go green)

18855 Disable event tracing templates in release mode (cla: yes, waiting for tree to go green)

18856 [web] running ios unit tests from felt … (cla: yes)

18858 [fuchsia] Add ability to configure separate data and asset dirs (cla: yes)

18859 add onDisplayOverlaySurface JNI (cla: yes, platform-android)