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The RelinquishGpuResource message from the browser process may
come before or after the rederer process closes it GPU channel.
As such, we need to wait until only the Browser GPU channel is
open until we can actually release the default off-screen
PBuffer surface and the EGL display.

This is a follow-up to https://codereview.chromium.org/712343003

Bug: 18724066
BUG=432268

Review URL: https://codereview.chromium.org/800103005

Cr-Commit-Position: refs/heads/master@{#308468}