28635 Roll Dart SDK from 25f8064d7387 to 05661056d153 (1 revision) (cla: yes, waiting for tree to go green)

28637 Roll Skia from 720674e1190d to 0c5b05c3ab53 (2 revisions) (cla: yes, waiting for tree to go green)

28638 Roll Skia from 0c5b05c3ab53 to 398ef4487b2a (7 revisions) (cla: yes, waiting for tree to go green)

28639 Enable compressed pointers on Android for 64 bit architectures. (cla: yes)

28640 [flutter_releases] Flutter beta 2.6.0-5.2.pre Engine Cherrypicks (cla: yes)