This fixes an edge case when the app clears both color and depth at the
same time when a color mask is set. It also handles stencil clear, but
does not handle stencil masks.

Includes test suppressions for a few platforms that may have driver
bugs.

Bug: angleproject:2455
Bug: angleproject:2547
Bug: angleproject:2548
Change-Id: I5ac0a461a075328e5fc4e5e262c4d21f68f93434
Reviewed-on: https://chromium-review.googlesource.com/1052072Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Luc Ferron <lucferron@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>