8780 VirtualDisplay size constraint - add a comment explaining the reason (cla: yes)

8789 Roll to branched dart sdk with hotfix(dartbug.com/36772) for flutter 1.5.4 (cla: yes)

8790 Roll to branched dart sdk with two more hotfixes for flutter 1.5.4. (cla: yes)

8792 Re-create texture from pixel buffer onGrContextCreate (cla: yes)

8793 Roll buildroot to pull in Fuchsia SDK related updates. (cla: yes)

8796 Dart SDK roll for 2019-04-30 (cla: yes)

PRs closed in this release of flutter/plugins