Return resources immediately after a Surface is destroyed

cc/surfaces/surface_observer.h

Index: cc/surfaces/surface_observer.h
diff --git a/cc/surfaces/surface_observer.h b/cc/surfaces/surface_observer.h
index e1c182a45c50d99b91c1a6940dd96f160d95b42f..9b2fc1c57f620fa11ca43813e65c74ef5fcc361e 100644
--- a/cc/surfaces/surface_observer.h
+++ b/cc/surfaces/surface_observer.h
@@ -18,6 +18,9 @@ class SurfaceObserver {
   // Runs when a Surface is damaged. *changed should be set to true if this
   // causes a Display to be damaged.
   virtual void OnSurfaceDamaged(const SurfaceId& surface_id, bool* changed) = 0;
+
+  // Called when a surface is garbage-collected.
+  virtual void OnSurfaceDiscarded(const SurfaceId& surface_id) = 0;
 };
 
 }  // namespace cc