[PPAPI] Add browser tests for compositor API

ppapi/proxy/compositor_layer_resource.h

Index: ppapi/proxy/compositor_layer_resource.h
diff --git a/ppapi/proxy/compositor_layer_resource.h b/ppapi/proxy/compositor_layer_resource.h
index fafaa98597804ac5af6e14ae9737644da77b6f58..33e98929654d5b96565fd7ca0103e261f0fafa5b 100644
--- a/ppapi/proxy/compositor_layer_resource.h
+++ b/ppapi/proxy/compositor_layer_resource.h
@@ -26,7 +26,7 @@ class PPAPI_PROXY_EXPORT CompositorLayerResource
 
   CompositorLayerResource(Connection connection,
                           PP_Instance instance,
-                          const CompositorResource* compositor);
+                          scoped_refptr<CompositorResource> compositor);
 
   const CompositorLayerData& data() const { return data_; }
   const ReleaseCallback& release_callback() const {
@@ -76,7 +76,7 @@ class PPAPI_PROXY_EXPORT CompositorLayerResource
 
   // The CompositorResource which own the layer. The layer is invalidated if
   // compositor_ is NULL.
-  const CompositorResource* compositor_;
+  scoped_refptr<CompositorResource> compositor_;
 
   // Release callback for uncommitted texture or image. When CommitLayers() on
   // the compositor_ is called, the callback will be copied into a map in the