Move swizzle & modulation computation, non-virtual functions onto
GrGLShaderBuilder. This lets us access all the default computations
when there's no GrCustomStage specified, and means that GrGLProgramStage
is effectively an interface class, all of whose functions can/should
be overriden.

http://codereview.appspot.com/6242051/



git-svn-id: http://skia.googlecode.com/svn/trunk@4045 2bbb7eff-a529-9590-31e7-b0007b416f81
6 files changed