Revert r1829: Fix failure to recover from GPU hang.

It's causing trouble with Aura. Locking the screen seems to generate the display mode change device status and Aura cannot recover.

http://crbug.com/178148
Review URL: https://codereview.appspot.com/7398052

git-svn-id: http://angleproject.googlecode.com/svn/trunk@1834 736b8ea6-26fd-11df-bfd4-992fa37f6226