cc: Add OutputSurface state snapshots.

cc/test/fake_output_surface_client.h

 // Copyright 2013 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 CC_TEST_FAKE_OUTPUT_SURFACE_CLIENT_H_
 #define CC_TEST_FAKE_OUTPUT_SURFACE_CLIENT_H_
 
 #include "cc/output/output_surface_client.h"
 
 namespace cc {
 
 class FakeOutputSurfaceClient : public OutputSurfaceClient {
  public:
   FakeOutputSurfaceClient() = default;
 
   void SetNeedsRedrawRect(const gfx::Rect& damage_rect) override {}
   void DidReceiveSwapBuffersAck() override;
   void DidReceiveTextureInUseResponses(
       const gpu::TextureInUseResponses& responses) override {}
+  void ReadbackSwappedOverlayTextures(
+      std::vector<SkBitmap>* bitmaps,
+      const base::Callback<void(bool)>& callback) override {}
 
   int swap_count() { return swap_count_; }
 
  private:
   int swap_count_ = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_OUTPUT_SURFACE_CLIENT_H_