Use asNewCustomStage instead of asABitmap in SkGpuDevice, also removed now-unecessary twoPointRadialParams parameter from asABitmap.

In SkGpuDevice we still fall back on using asABitmap for effects that don't have asNewCustomStage implemented, but it still simplifies things a fair amount.
Review URL: https://codereview.appspot.com/6430060

git-svn-id: http://skia.googlecode.com/svn/trunk@4755 2bbb7eff-a529-9590-31e7-b0007b416f81
11 files changed