19338 Roll Dart SDK from e24733ebd16c to 243ad5427564 (5 revisions) (cla: yes, waiting for tree to go green)

19339 Fix broken mac/fuchsia compiles (affects: tests, cla: yes, platform-android, platform-fuchsia, platform-ios, platform-linux, platform-macos, platform-windows)

19341 Cache CanvasKit objects and delete if not used. (cla: yes)

19342 Roll Dart SDK from 243ad5427564 to 7fc61e77e225 (5 revisions) (cla: yes, waiting for tree to go green)

19343 Roll Fuchsia Mac SDK from YGK_M… to l3tHO… (cla: yes, waiting for tree to go green)