This is useful for testing context lost behaviour.

BUG=angleproject:3379

Change-Id: If0e1538553b1761e313fc36ccde5138cd495200f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1566141
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>