Optimize Canvas fill and drawImage with SourceIn, DestinationIn, SourceOut, and Desti...

Optimize Canvas fill and drawImage with SourceIn, DestinationIn, SourceOut, and DestinationAtop using transparencyLayer.
https://bugs.webkit.org/show_bug.cgi?id=79659

Patch by Dirk Schulze <krit@webkit.org> on 2014-04-11
Reviewed by Andreas Kling.

Add performance tests for fillRect() and drawImage() on composited contexts.

* Canvas/compositing-drawimage.html: Added.
* Canvas/compositing-fillRect.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@167123 268f45cc-cd09-0410-ab3c-d52691b4dbfc