Add standard way to indicate GM is GPU-only.

gm/beziereffects.cpp

Index: gm/beziereffects.cpp
diff --git a/gm/beziereffects.cpp b/gm/beziereffects.cpp
index e49fc91a86ee4d55c508b0fd1e004c9f07a22823..0ddcc52b95da2de9c37acb51ec594885fb2a37ad 100644
--- a/gm/beziereffects.cpp
+++ b/gm/beziereffects.cpp
@@ -48,6 +48,7 @@ protected:
     void onDraw(SkCanvas* canvas) SK_OVERRIDE {
         GrRenderTarget* rt = canvas->internal_private_accessTopLayerRenderTarget();
         if (NULL == rt) {
+            this->drawGpuOnlyMessage(canvas);
             return;
         }
         GrContext* context = rt->getContext();
@@ -203,6 +204,7 @@ protected:
     void onDraw(SkCanvas* canvas) SK_OVERRIDE {
         GrRenderTarget* rt = canvas->internal_private_accessTopLayerRenderTarget();
         if (NULL == rt) {
+            this->drawGpuOnlyMessage(canvas);
             return;
         }
         GrContext* context = rt->getContext();
@@ -391,6 +393,7 @@ protected:
     void onDraw(SkCanvas* canvas) SK_OVERRIDE {
         GrRenderTarget* rt = canvas->internal_private_accessTopLayerRenderTarget();
         if (NULL == rt) {
+            this->drawGpuOnlyMessage(canvas);
             return;
         }
         GrContext* context = rt->getContext();