Merge 125445 - [chromium] Clear HUD canvas contents before drawing into it.

Merge 125445 - [chromium] Clear HUD canvas contents before drawing into it.
https://bugs.webkit.org/show_bug.cgi?id=93759

Reviewed by Adrienne Walker.

Not clearing the bitmaps before drawing into it results into
random noise. This patch also caches the SkCanvas used by the HUD
to avoid reallocating it every frame.

* platform/graphics/chromium/cc/CCHeadsUpDisplayLayerImpl.cpp:
(WebCore::CCHeadsUpDisplayLayerImpl::willDraw):
* platform/graphics/chromium/cc/CCHeadsUpDisplayLayerImpl.h:


TBR=vangelis@chromium.org
Committed: https://trac.webkit.org/changeset/126822