Expand modulate, add, subtract, extract component glsl helpers.

include/gpu/GrTypesPriv.h

Index: include/gpu/GrTypesPriv.h
===================================================================
--- include/gpu/GrTypesPriv.h	(revision 8735)
+++ include/gpu/GrTypesPriv.h	(working copy)
@@ -48,6 +48,8 @@
     GR_STATIC_ASSERT(GR_ARRAY_COUNT(kCounts) == kGrSLTypeCount);
 }
 
+/** Return the type enum for a vector of floats of length n (1..4),
+ e.g. 1 -> kFloat_GrSLType, 2 -> kVec2_GrSLType, ... */
 static inline GrSLType GrSLFloatVectorType(int count) {
     GrAssert(count > 0 && count <= 4);
     return (GrSLType)(count);