Pass GrCustomStage to key-generation functions and emitCode().

R=robertphillips@google.com
Review URL: https://codereview.appspot.com/6819046

git-svn-id: http://skia.googlecode.com/svn/branches/gpu_dev@6182 2bbb7eff-a529-9590-31e7-b0007b416f81
30 files changed