Avoid record-time rasterization of gradient patterns.

We already have an uncached path for large tiles:
GeneratorGeneratedImage::drawPatternWithoutCache().

Not only does that fallback avoid record time rasterization, but it turns
out it's actually much faster than drawing into an ImageBuffer and
caching the tile! A modified version of
http://themaninblue.com/experiment/AnimationBenchmark/svg/ with
the following <body> style shows an almost 2x framerate increase:
body
{
  -webkit-border-image: -webkit-repeating-linear-gradient(30deg, black 10%, white 20%) 10 10 10 10 repeat repeat;
}

  * ImageBuffer/cached tile frame rate: ~97fps (http://i.imgur.com/tlES49f.png)
  * native tiling frame rate: ~186fps (http://i.imgur.com/eqgGm8G.png)

This CL rips out the ImageBuffer caching logic and related methods.

About 30 pixel tests require minor rebaselines.

Review URL: https://codereview.chromium.org/27582002

git-svn-id: svn://svn.chromium.org/blink/trunk@159891 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert "Revert "Make composited scrolling codepaths co-operate.""

This reverts commit c48a005859152716e9c731fc8c686e98d04fba69.

This was speculatively reverted, but it turned out not to be the culprit. Relanding.

R=hartmanng@chromium.org
BUG=306566

Review URL: https://codereview.chromium.org/26253006

git-svn-id: svn://svn.chromium.org/blink/trunk@159892 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert "Revert "[CSS Blending] Implement mix-blend-mode in software.""

This reverts commit 53377cb4ebf1aedfa567427fa1096fa0c2194993.

This was a speculative revert, but didn't turn out to be the culprit. Relanding.

TBR=mitica@adobe.com
BUG=306566

Review URL: https://codereview.chromium.org/27748002

git-svn-id: svn://svn.chromium.org/blink/trunk@159893 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Clean up Document::renderView()

Instead of shadowing the implementations of Document::renderer() and
setRenderer() we manually manage the m_renderView pointer. This is
cleaner and less confusing since setRenderer(0) doesn't do something
special inside Document compared to normal Nodes.

This is in preparation to making Document::renderer() private and
forcing everyone to use ::renderView().

This is part of the reverted r159188 that was not an issue.

Review URL: https://codereview.chromium.org/27474004

git-svn-id: svn://svn.chromium.org/blink/trunk@159894 bbb929c8-8fbe-4397-9dbb-9b2b20218538