Add ScopedAllowWait to TaskGraphRunner to Avoid Crash in Shutdown

When shutting down, TaskGraphRunner will clear out tasks that are ready
to run and wait for running tasks to finish running. Wait is disallowed
in main thread and crashes in single thread impl-side painting.

R=danakj, jam, brettw
BUG=369653

Review URL: https://codereview.chromium.org/946103004

Cr-Commit-Position: refs/heads/master@{#318265}


CrOS-Libchrome-Original-Commit: 0471c66927ca0c21a0785174ef3fe245b9908766
1 file changed
tree: 4b1091a06ad34f0ac8bcf63d1548123a56ca99f5
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/