plus add a bench and unittest for it. git-svn-id: http://skia.googlecode.com/svn/trunk@3989 2bbb7eff-a529-9590-31e7-b0007b416f81
git-svn-id: http://skia.googlecode.com/svn/trunk@2985 2bbb7eff-a529-9590-31e7-b0007b416f81