Improve GPU software rendering list histograms.
Improve GPU software rendering list histograms.

Implements per feature histograms.  At the moment three features: accelerated-compositing, accelerated-2d-canvas, and webgl.  Also, implemented each feature's allowed case percentage, per each OS (under Windows, they are divided into XP, Vista, and Win7).

BUG=91875
TEST=none 
Review URL: http://codereview.chromium.org/7618050

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@98840 0039d316-1c4b-4281-b951-d872f2087c98

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