Use coverage stages for supersample AA resolve, edgeAA, and glyph masks. Expose a mask stage through GrPaint

Review URL: http://codereview.appspot.com/4548048/



git-svn-id: http://skia.googlecode.com/svn/trunk@1356 2bbb7eff-a529-9590-31e7-b0007b416f81
7 files changed