[DesktopCapturer] FallbackDesktopCapturerWrapper and its tests

webrtc/modules/desktop_capture/desktop_capturer_differ_wrapper.h

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_MODULES_DESKTOP_CAPTURE_DESKTOP_CAPTURER_DIFFER_WRAPPER_H_
 #define WEBRTC_MODULES_DESKTOP_CAPTURE_DESKTOP_CAPTURER_DIFFER_WRAPPER_H_
 
 #include <memory>
 
 #include "webrtc/modules/desktop_capture/desktop_capturer.h"
 #include "webrtc/modules/desktop_capture/shared_desktop_frame.h"
 
 namespace webrtc {
 
 // DesktopCapturer wrapper that calculates updated_region() by comparing frames
 // content. This class always expects the underlying DesktopCapturer
 // implementation returns a superset of updated regions in DestkopFrame. If a
 // DesktopCapturer implementation does not know the updated region, it should
 // set updated_region() to full frame.
 //
 // This class marks entire frame as updated if the frame size or frame stride
 // has been changed.
-class DesktopCapturerDifferWrapper : public DesktopCapturer,
-                                     public DesktopCapturer::Callback {
+class DesktopCapturerDifferWrapper final : public DesktopCapturer,
+                                           private DesktopCapturer::Callback {

[Jamie, 2017/02/15 18:43:48]

IIRC, private inheritance is not allowed in Chromium; either make it public or
use a member variable
(https://google.github.io/styleguide/cppguide.html#Inheritance).

TBH, this feels like a legitimate use of private inheritance (a member variable
is overkill, yet there's no value in exposing the inheritance to callers), so
I'll defer to Sergey on this.

[Hzj_jie, 2017/02/15 21:20:36]

I have not noticed this guide. Since using private inheritance is actively
disallowed, I will undo the change to this file.

  public:
   // Creates a DesktopCapturerDifferWrapper with a DesktopCapturer
   // implementation, and takes its ownership.
   explicit DesktopCapturerDifferWrapper(
       std::unique_ptr<DesktopCapturer> base_capturer);
 
   ~DesktopCapturerDifferWrapper() override;
 
   // DesktopCapturer interface.
   void Start(DesktopCapturer::Callback* callback) override;
@@ skipping 11 matching lines @@
                        std::unique_ptr<DesktopFrame> frame) override;
 
   const std::unique_ptr<DesktopCapturer> base_capturer_;
   DesktopCapturer::Callback* callback_;
   std::unique_ptr<SharedDesktopFrame> last_frame_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_DESKTOP_CAPTURER_DIFFER_WRAPPER_H_