Add/remove surface references via MojoCompositorFrameSink.

services/ui/ws/test_server_window_delegate.h

 // Copyright 2014 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_TEST_SERVER_WINDOW_DELEGATE_H_
 #define SERVICES_UI_WS_TEST_SERVER_WINDOW_DELEGATE_H_
 
 #include "base/macros.h"
+#include "cc/surfaces/surface_id.h"
 #include "services/ui/ws/server_window_delegate.h"
 
 namespace cc {
 namespace mojom {
 class DisplayCompositor;
 }
 }
 
 namespace ui {
-
 namespace ws {
 
 class TestServerWindowDelegate : public ServerWindowDelegate {
  public:
   TestServerWindowDelegate();
   ~TestServerWindowDelegate() override;
 
   void set_root_window(ServerWindow* window) { root_window_ = window; }
 
  private:
   // ServerWindowDelegate:
   cc::mojom::DisplayCompositor* GetDisplayCompositor() override;
+  const cc::SurfaceId& GetRootSurfaceId() const override;
   ServerWindow* GetRootWindow(const ServerWindow* window) override;
 
-  ServerWindow* root_window_;
+  cc::SurfaceId root_surface_id_;
+  ServerWindow* root_window_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(TestServerWindowDelegate);
 };
 
 }  // namespace ws
-
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_TEST_SERVER_WINDOW_DELEGATE_H_