Add SurfaceWillDraw notification

cc/surfaces/surface_manager.h

Index: cc/surfaces/surface_manager.h
diff --git a/cc/surfaces/surface_manager.h b/cc/surfaces/surface_manager.h
index 01d18b2dc1986ca3c0f22aad6105610916b313a5..31357b8654b6f09a901d12b0ae1e527b59a84ce3 100644
--- a/cc/surfaces/surface_manager.h
+++ b/cc/surfaces/surface_manager.h
@@ -74,6 +74,10 @@ class CC_SURFACES_EXPORT SurfaceManager {
   // Destroy the Surface once a set of sequence numbers has been satisfied.
   void DestroySurface(std::unique_ptr<Surface> surface);
 
+  // Called when a surface has been added to the Display Frame and will

[danakj, 2017/06/14 18:53:12]

Display Frame is written like it is a type, but I don't think it is. You're
referring to the aggregated CompositorFrame in the Display, I believe.

[gklassen, 2017/06/14 19:29:11]

Good call.  Your suggestion makes the description clearer.  Thank you. 
 
Done.

+  // invoke observers with the OnSurfaceWillDraw notification.
+  void SurfaceWillDraw(const SurfaceId& surface_id);
+
   Surface* GetSurfaceForId(const SurfaceId& surface_id);
 
   void AddObserver(SurfaceObserver* obs) { observer_list_.AddObserver(obs); }