Fixed DCHECK in InProcessGpuThread shutdown.

Fixed DCHECK in InProcessGpuThread shutdown.

Upon BrowserMainRunner::Shutdown(), InProcessGpuThread sometimes (race condition)
terminates simply by exiting the message loop due to closed RPC channel, the
ThreadWasQuitProperly flag is required to signal correct termnation in this
case.

BUG=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=275848

[Victor Starodub, 2014-06-06 15:45:55]

I need this to implement desktop-like shutdown logic for content_browsertests on
android.

For context: https://codereview.chromium.org/311943002/ -- this contains all the
changes to the text fixture and other changes required to implement correct
shutdown on android. I'm currently splitting this change into smaller more
reviewable parts.

[Ken Russell (switch to Gerrit), 2014-06-06 19:51:40]

This looks fine to me but sievers or aelias should look at it as this only
affects Android.

[no sievers, 2014-06-06 19:56:15]

lgtm

[Ken Russell (switch to Gerrit), 2014-06-06 20:00:08]

LGTM too.

[Victor Starodub, 2014-06-09 12:54:06]

The CQ bit was checked by starodub@google.com

[commit-bot: I haz the power, 2014-06-09 12:54:59]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/starodub@google.com/323513003/1

[Victor Starodub, 2014-06-09 16:54:16]

The CQ bit was unchecked by starodub@google.com

[Victor Starodub, 2014-06-09 16:54:17]

The CQ bit was checked by starodub@google.com

[commit-bot: I haz the power, 2014-06-09 16:55:13]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/starodub@google.com/323513003/1

[commit-bot: I haz the power, 2014-06-09 20:25:06]

Change committed as 275848