Wrap ScreenCapturer with ScreenCapturerDifferWrapper

webrtc/modules/desktop_capture/win/screen_capturer_win_directx.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.
  */
 
@@ skipping 10 matching lines @@
 #include "webrtc/modules/desktop_capture/screen_capture_frame_queue.h"
 #include "webrtc/modules/desktop_capture/shared_desktop_frame.h"
 #include "webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h"
 
 namespace webrtc {
 
 // ScreenCapturerWinDirectx captures 32bit RGBA using DirectX. This
 // implementation won't work when ScreenCaptureFrameQueue.kQueueLength is not 2.
 class ScreenCapturerWinDirectx : public ScreenCapturer {
  public:
-  // Whether the system support DirectX based capturing.
+  // Whether the system supports DirectX based capturing.
   static bool IsSupported();
 
-  explicit ScreenCapturerWinDirectx(const DesktopCaptureOptions& options);
+  // Creates a ScreenCapturer which uses DirectX APIs to capture screen. Returns
+  // nullptr if the system does not support DirectX duplication APIs.
+  static std::unique_ptr<ScreenCapturer> Create(
+      const DesktopCaptureOptions& options);
+
   virtual ~ScreenCapturerWinDirectx();
 
   void Start(Callback* callback) override;
   void SetSharedMemoryFactory(
       std::unique_ptr<SharedMemoryFactory> shared_memory_factory) override;
   void Capture(const DesktopRegion& region) override;
   bool GetScreenList(ScreenList* screens) override;
   bool SelectScreen(ScreenId id) override;
 
  private:
+  explicit ScreenCapturerWinDirectx(const DesktopCaptureOptions& options);
+
   // Returns desktop size of selected screen.
   DesktopSize SelectedDesktopSize() const;
 
   ScreenCaptureFrameQueue<SharedDesktopFrame> frames_;
   std::unique_ptr<SharedMemoryFactory> shared_memory_factory_;
   Callback* callback_ = nullptr;
 
   DxgiDuplicatorController::Context context_;
 
   ScreenId current_screen_id = kFullDesktopScreenId;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(ScreenCapturerWinDirectx);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_WIN_SCREEN_CAPTURER_WIN_DIRECTX_H_