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ScopedMakeCurrent and ScopedReleaseCurrent don't check for errors when
restoring the previous context. In most cases the MakeCurrent that
restores the previous context should not fail, and if it fails we don't
return errors up the stack so we CHECK that MakeCurrent succeeds.

However, for DirectComposition, we use ScopedReleaseCurrent when
reallocating the drawing surface. Restoring the context can fail in this
case. This CL adds a Restore method to both classes whose return value
must be handled. This prevents the CHECK in the destructor.

The lack of error checking is causing a crash in SetSwapInterval, due to
null-dereference of GLContext::GetCurrent. This was found by adding a
crash key to get the stack trace for SetCurrent(NULL).

BUG=724999
R=piman

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I370ff470c78afa76bd000de60a6a63295746ee1b
Reviewed-on: https://chromium-review.googlesource.com/818533Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523562}