18707 Roll Skia from 8c5786622b4e to 502eab4fc913 (2 revisions) (cla: yes, waiting for tree to go green)

18709 Pass SurfaceFrame to SubmitFrame (cla: yes)

18713 Make GetAllocationSize const (cla: yes, waiting for tree to go green)

18714 [fuchsia] NNBD: Kernel libraries for Flutter, Dart runners (cla: yes)

18717 Roll Fuchsia Mac SDK from WuG3u… to YmMjL… (cla: yes, waiting for tree to go green)

18719 Add braces around multi-line branches to match code style (cla: yes)

18721 Add an engine PR template (cla: yes)