This prevents races between the application's connection and ANGLE's one
that could lead to X errors crashing the program.

BUG=angleproject:892

Change-Id: Ic09462e76724d1a32c35b32708de97258d99241c
Reviewed-on: https://chromium-review.googlesource.com/271178Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>