Merge 148856 "Disable solid background color optimization for composited layers."

Merge 148856 "Disable solid background color optimization for composited layers."

> Disable solid background color optimization for composited layers.
> 
> This has two parts:
> 1.) Return false from GraphicsLayer::supportsBackgroundColorContent() so that RenderLayerBacking always paints the background
> 2.) Make GraphicsLayer::setContentsToSolidColor() a no-op so we don't mess with
> the content layer, since this is called unconditionally.
> 
> This restores the behavior from m26 and before.
> 
> TBR=apatrick@chromium.org
> BUG=232846
> 
> Review URL: https://codereview.chromium.org/14407003

TBR=jamesr@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=149029

[jamesr, 2013-04-24 19:36:21]

Committed patchset #1 manually as r149029 (presubmit successful).