If the context is lost due to an OUT_OF_MEMORY error, it was
impossible to check the error.

BUG=angleproject:1309

Change-Id: I50fbd46b139d44774dde804445f12b8d34d73e29
Reviewed-on: https://chromium-review.googlesource.com/521203Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>