Call GetGlobalContext instead of GetValidGlobalContext for gl::GetError 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/521203 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>