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
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=148856

[jamesr, 2013-04-22 21:30:29]

I'm landing this patch for Al - the patch is actually by him and reviewed by me.
 We couldn't use Al's rietveld issue because he doesn't have a full blink
checkout and the intrastructure can't handle base URLs that aren't the root of
the repo

[jamesr, 2013-04-22 21:31:50]

Committed patchset #1 manually as r148856 (presubmit successful).

[eseidel, 2013-04-25 06:51:22]

It's not at all clear to me from the description "why".