Allow GrEffects with multiple textures.

It will work as long as the total number of textures sis less than GrDrawState::kNumStages. That will be fixed in a follow up CL.
Review URL: https://codereview.appspot.com/7040052

git-svn-id: http://skia.googlecode.com/svn/trunk@7023 2bbb7eff-a529-9590-31e7-b0007b416f81
10 files changed