Stocks app shouldn't show black when resuming from recents list

sky/shell/ui_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 SKY_SHELL_UI_DELEGATE_H_
 #define SKY_SHELL_UI_DELEGATE_H_
 
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "sky/services/viewport/viewport_observer.mojom.h"
 #include "ui/gfx/geometry/size.h"
+#include "ui/gfx/native_widget_types.h"
 
 namespace sky {
 namespace shell {
 
 class UIDelegate {
  public:
   virtual void ConnectToViewportObserver(
       mojo::InterfaceRequest<ViewportObserver> request) = 0;
+  virtual void OnAcceleratedWidgetAvailable(gfx::AcceleratedWidget widget) = 0;
+  virtual void OnOutputSurfaceDestroyed() = 0;
 
  protected:
   virtual ~UIDelegate();
 };
 
 }  // namespace shell
 }  // namespace sky
 
 #endif  // SKY_SHELL_UI_DELEGATE_H_