This is another warning turned on in Skia. It enforces an explicit
copy assignment operator in some implicitly-generated cases. It
caught one potential error in SubresourceUpdate.

Bug: skia:7647
Change-Id: Ia501f619cf7f3d2e8647cdbbda2936f51f9721ba
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2381953
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>