Move VertexBuilder to a GrGLFullShaderBuilder subclass

src/gpu/gl/GrGLProgramDesc.h

Index: src/gpu/gl/GrGLProgramDesc.h
diff --git a/src/gpu/gl/GrGLProgramDesc.h b/src/gpu/gl/GrGLProgramDesc.h
index e160438e08c0b137cfce0cd2930051161b253000..0c7c8cf629949c875ee8cbdb501fb7a3ab4e9a5d 100644
--- a/src/gpu/gl/GrGLProgramDesc.h
+++ b/src/gpu/gl/GrGLProgramDesc.h
@@ -113,6 +113,17 @@ private:
         kColorInputCnt
     };
 
+    static GrSLConstantVec KnownColorInputValue(ColorInput ci) {
+        switch (ci) {
+            case GrGLProgramDesc::kTransBlack_ColorInput:
+                return kZeros_GrSLConstantVec;
+            case GrGLProgramDesc::kSolidWhite_ColorInput:
+                return kOnes_GrSLConstantVec;
+            default:
+                return kNone_GrSLConstantVec;
+        }
+    }
+
     enum CoverageOutput {
         // modulate color and coverage, write result as the color output.
         kModulate_CoverageOutput,
@@ -221,6 +232,7 @@ private:
     // code generation to GrGLShaderBuilder (and maybe add getters rather than friending).
     friend class GrGLProgram;
     friend class GrGLShaderBuilder;
+    friend class GrGLFullShaderBuilder;
 };
 
 #endif