Fix failure to recover from device hang.

Sometimes IDirect3DDevice9Ex::CheckDeviceState returns S_PRESENT_MODE_CHANGED when the GPU has hung. It's not consistent, maybe one time out of two when I hang the GPU while running WebGL Aquarium.

This unfortunately means that changes to display mode will cause ANGLE to report context lost. Other ideas appreciated.
Review URL: https://codereview.appspot.com/7305093

git-svn-id: http://angleproject.googlecode.com/svn/trunk@1829 736b8ea6-26fd-11df-bfd4-992fa37f6226