Mus+Ash: Use standard cc mechanism for surface lifetime.

services/ui/ws/server_window_surface.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 SERVICES_UI_WS_SERVER_WINDOW_SURFACE_H_
 #define SERVICES_UI_WS_SERVER_WINDOW_SURFACE_H_
 
 #include <set>
 
 #include "base/macros.h"
@@ skipping 32 matching lines @@
     return last_submitted_frame_size_;
   }
 
   bool may_contain_video() const { return may_contain_video_; }
 
   // mojom::Surface:
   void SubmitCompositorFrame(
       cc::CompositorFrame frame,
       const SubmitCompositorFrameCallback& callback) override;
 
+  // There is a 1-1 correspondence between FrameSinks and frame sources.
+  // The FrameSinkId uniquely identifies the FrameSink, and since there is
+  // one FrameSink per ServerWindowSurface, it allows the window server
+  // to uniquely identify the window, and the thus the client that generated the
+  // frame.
+  const cc::FrameSinkId& frame_sink_id() const { return frame_sink_id_; }
+
+  // The LocalFrameId can be thought of as an identifier to a bucket of
+  // sequentially submitted CompositorFrames in the same FrameSink all sharing
+  // the same size and device scale factor.
   const cc::LocalFrameId& local_frame_id() const { return local_frame_id_; }
 
+  bool has_frame() const { return !local_frame_id_.is_null(); }
+
   cc::SurfaceId GetSurfaceId() const;
 
-  // Destroys old surfaces that have been outdated by a new surface.
-  void DestroySurfacesScheduledForDestruction();
+  ServerWindow* window();
 
  private:
-  ServerWindow* window();
 
   // SurfaceFactoryClient implementation.
   void ReturnResources(const cc::ReturnedResourceArray& resources) override;
   void SetBeginFrameSource(cc::BeginFrameSource* begin_frame_source) override;
 
   const cc::FrameSinkId frame_sink_id_;
 
   ServerWindowSurfaceManager* manager_;  // Owns this.
 
   gfx::Size last_submitted_frame_size_;
 
   cc::LocalFrameId local_frame_id_;
   cc::SurfaceIdAllocator surface_id_allocator_;
   cc::SurfaceFactory surface_factory_;
 
   mojom::SurfaceClientPtr client_;
   mojo::Binding<Surface> binding_;
 
-  // Set of surface ids that need to be destroyed.
-  std::set<cc::LocalFrameId> surfaces_scheduled_for_destruction_;
-
   bool may_contain_video_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(ServerWindowSurface);
 };
 
 }  // namespace ws
 
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_SERVER_WINDOW_SURFACE_H_