Bug 902929. Assert that we don't have a compositable child for ImageBridgeClients. r=nical

gfx/layers/client/CompositableClient.h

@@ -102,7 +102,7 @@ public:
   CompositableChild* GetIPDLActor() const;
 
   // should only be called by a CompositableForwarder
-  void SetIPDLActor(CompositableChild* aChild);
+  virtual void SetIPDLActor(CompositableChild* aChild);
 
   CompositableForwarder* GetForwarder() const
   {

gfx/layers/client/ImageClient.h

@@ -181,6 +181,11 @@ public:
     return TextureInfo(mType);
   }
 
+  virtual void SetIPDLActor(CompositableChild* aChild) MOZ_OVERRIDE
+  {
+    MOZ_ASSERT(!aChild, "ImageClientBridge should not have IPDL actor");
+  }
+
 protected:
   uint64_t mAsyncContainerID;
   ShadowableLayer* mLayer;