Add standard way to indicate GM is GPU-only.

gm/rrects.cpp

Index: gm/rrects.cpp
diff --git a/gm/rrects.cpp b/gm/rrects.cpp
index 046e5e624aa6d0f6d1d3b1033fcca8d17644e1c7..4b8e7648f72c23603d24353c4fb078457d5ba374 100644
--- a/gm/rrects.cpp
+++ b/gm/rrects.cpp
@@ -57,13 +57,15 @@ protected:
     SkISize onISize() SK_OVERRIDE { return SkISize::Make(kImageWidth, kImageHeight); }
 
     void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        GrContext* context = NULL;
 #if SK_SUPPORT_GPU
         GrRenderTarget* rt = canvas->internal_private_accessTopLayerRenderTarget();
-        GrContext* context = rt ? rt->getContext() : NULL;
+        context = rt ? rt->getContext() : NULL;
+#endif
         if (kEffect_Type == fType && NULL == context) {
+            this->drawGpuOnlyMessage(canvas);
             return;
         }
-#endif
 
         SkPaint paint;
         if (kAA_Draw_Type == fType) {