Release GPU resources only after renderer GPU channels are closed.

Release GPU resources only after renderer GPU channels are closed.

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
Committed: https://crrev.com/aec301ce2f19d24b7e7e4033f041e47b7c3820cb
Cr-Commit-Position: refs/heads/master@{#308468}

[GusFernandez, 2014-12-15 20:14:30]

gusfernandez@chromium.org changed reviewers:
+ byungchul@chromium.org, gunsch@chromium.org, jbauman@chromium.org,
lcwu@chromium.org

[GusFernandez, 2014-12-15 21:46:25]

gusfernandez@chromium.org changed reviewers:
+ dcheng@chromium.org, piman@chromium.org

[piman, 2014-12-15 21:51:37]

lgtm

[GusFernandez, 2014-12-15 22:08:17]

+halliwell

[GusFernandez, 2014-12-15 22:08:30]

The CQ bit was checked by gusfernandez@chromium.org

[commit-bot: I haz the power, 2014-12-15 22:09:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/800103005/1

[commit-bot: I haz the power, 2014-12-16 00:07:41]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-16 00:08:39]

Patchset 1 (id:??) landed as
https://crrev.com/aec301ce2f19d24b7e7e4033f041e47b7c3820cb
Cr-Commit-Position: refs/heads/master@{#308468}