Simply check if the device has already been lost.  Chrome already checks
glGetGraphicsResetStatus after SwapBuffers and MakeCurrent.

BUG=angleproject:1472
BUG=621240

Change-Id: I95fe6306fa0c09191a4b1b93840c2143e069ef53
Reviewed-on: https://chromium-review.googlesource.com/1026527
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>