This is another warning required by Skia. This one didn't find
anything that surprising. Enabling the warning does help enforce
code consistency and avoids a bit of possible undefined behaviour.

Bug: angleproject:4046
Change-Id: Ifec7f4afad49cd820bf3c0a79df3f46559473ee2
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1877477
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>