Move GrGLInterface function pointers into a nested struct

include/gpu/gl/SkGLContextHelper.h

Index: include/gpu/gl/SkGLContextHelper.h
diff --git a/include/gpu/gl/SkGLContextHelper.h b/include/gpu/gl/SkGLContextHelper.h
index e83fd159047bdb48449543e291839af95e56e493..ea940c8bc05e2590e5daa86ea2482ec4650d6c77 100644
--- a/include/gpu/gl/SkGLContextHelper.h
+++ b/include/gpu/gl/SkGLContextHelper.h
@@ -77,11 +77,11 @@ private:
  * Helper macros for using the GL context through the GrGLInterface. Example:
  * SK_GL(glCtx, GenTextures(1, &texID));
  */
-#define SK_GL(ctx, X) (ctx).gl()->f ## X;    \
-                      SkASSERT(GR_GL_NO_ERROR == (ctx).gl()->fGetError())
-#define SK_GL_RET(ctx, RET, X) (RET) = (ctx).gl()->f ## X;    \
-                  SkASSERT(GR_GL_NO_ERROR == (ctx).gl()->fGetError())
-#define SK_GL_NOERRCHECK(ctx, X) (ctx).gl()->f ## X
-#define SK_GL_RET_NOERRCHECK(ctx, RET, X) (RET) = (ctx).gl()->f ## X
+#define SK_GL(ctx, X) (ctx).gl()->fFunctions.f ## X;    \
+                      SkASSERT(GR_GL_NO_ERROR == (ctx).gl()->fFunctions.fGetError())
+#define SK_GL_RET(ctx, RET, X) (RET) = (ctx).gl()->fFunctions.f ## X;    \
+                  SkASSERT(GR_GL_NO_ERROR == (ctx).gl()->fFunctions.fGetError())
+#define SK_GL_NOERRCHECK(ctx, X) (ctx).gl()->fFunctions.f ## X
+#define SK_GL_RET_NOERRCHECK(ctx, RET, X) (RET) = (ctx).gl()->fFunctions.f ## X
 
 #endif