Add a state bit to GrDrawState that forces coverage to be blended.

Use this mode in GrClipMaskManager.

R=robertphillips@google.com
Review URL: https://codereview.appspot.com/6945048

git-svn-id: http://skia.googlecode.com/svn/trunk@6790 2bbb7eff-a529-9590-31e7-b0007b416f81
4 files changed