Add CreateWindowCapturer() and CreateScreenCapturer() in DesktopCapturer

webrtc/modules/desktop_capture/screen_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_SCREEN_CAPTURER_DIFFER_WRAPPER_H_
 #define WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURER_DIFFER_WRAPPER_H_
 
 #include <memory>
 
 #include "webrtc/modules/desktop_capture/screen_capturer.h"
 #include "webrtc/modules/desktop_capture/shared_desktop_frame.h"
 
 namespace webrtc {
 
+// TODO(zijiehe): Remove, use DesktopCapturerDifferWrapper.
 // ScreenCapturer wrapper that calculates updated_region() by comparing frames
 // content. This class always expects the underlying ScreenCapturer
 // implementation returns a superset of updated regions in DestkopFrame. If a
 // ScreenCapturer 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 ScreenCapturerDifferWrapper : public ScreenCapturer,
                                     public DesktopCapturer::Callback {
@@ skipping 18 matching lines @@
                        std::unique_ptr<DesktopFrame> frame) override;
 
   const std::unique_ptr<ScreenCapturer> base_capturer_;
   DesktopCapturer::Callback* callback_;
   std::unique_ptr<SharedDesktopFrame> last_frame_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURER_DIFFER_WRAPPER_H_