Android: Attach hidden layer for CopyFromCompositingSurface()

ui/android/window_android_compositor.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 UI_ANDROID_WINDOW_ANDROID_COMPOSITOR_H_
 #define UI_ANDROID_WINDOW_ANDROID_COMPOSITOR_H_
 
 #include <memory>
 
 #include "cc/output/copy_output_request.h"
 #include "ui/android/ui_android_export.h"
 
 namespace cc {
 class Layer;
 }
 
 namespace ui {
 
 class ResourceManager;
 
 // Android interface for compositor-related tasks.
 class UI_ANDROID_EXPORT WindowAndroidCompositor {
  public:
   virtual ~WindowAndroidCompositor() {}
 
+  virtual void AttachLayerForReadback(scoped_refptr<cc::Layer> layer) = 0;
   virtual void RequestCopyOfOutputOnRootLayer(
       std::unique_ptr<cc::CopyOutputRequest> request) = 0;
   virtual void OnVSync(base::TimeTicks frame_time,
                        base::TimeDelta vsync_period) = 0;
   virtual void SetNeedsAnimate() = 0;
   virtual ResourceManager& GetResourceManager() = 0;
 };
 
 }  // namespace ui
 
 #endif  // UI_ANDROID_WINDOW_ANDROID_COMPOSITOR_H_