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Seems that we may not get the webglcontextlost event unless a GL command
happens to fail after the context loss has occurred. Use a 250ms timer
to tickle the context until the webglcontextlost event occurs.

BUG=929012,929429

Change-Id: I191b2338f633612fc3b8206bf27f9a14c968bd23
Reviewed-on: https://chromium-review.googlesource.com/c/1459780
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630134}