On some Intel D3D drivers on Skylake, calling clear may take no effect.
To work around this bug, we call clear() twice when we attempt to do clear
on these platforms.

BUG=chromium:655534

Change-Id: I3b05892e80e5797d268861e8f52e080f5175855b
Reviewed-on: https://chromium-review.googlesource.com/398522
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>