Worker: Return early in TaskWorklet/WorkerTaskQueue::postTask() after context destruction

Bug: 965283
Change-Id: Ia8a959a8ed2d5423231001ea59957d09652caf2d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1624007
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662112}
4 files changed