exo: Add support for subcompositor interface.

components/exo/surface_delegate.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_EXO_SURFACE_DELEGATE_H_
 #define COMPONENTS_EXO_SURFACE_DELEGATE_H_
 
 namespace exo {
 
 // Handles events on surfaces in context-specific ways.
 class SurfaceDelegate {
  public:
-  // Called when the surface is destroyed. The delegate can use this
-  // opportunity to delete itself if necessary.
-  virtual void OnSurfaceDestroying() = 0;
-
   // Called when surface was requested to commit all double-buffered state.
   virtual void OnSurfaceCommit() = 0;
 
+  // Returns true if surface is in synchronized mode. ie. commit of
+  // double-buffered state should be synchronized with parent surface.
+  virtual bool IsSurfaceSynchronized() const = 0;
+
  protected:
   virtual ~SurfaceDelegate() {}
 };
 
 }  // namespace exo
 
 #endif  // COMPONENTS_EXO_SURFACE_DELEGATE_H_