Use std::unique_ptr<> to pass frame ownership in DesktopCapturer impls.

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 64 matching lines @@
   // ProcessFrame will insert a whole desktop size as updated region instead.
   static bool DetectUpdatedRegion(const DXGI_OUTDUPL_FRAME_INFO& frame_info,
                                   DesktopRegion* updated_region);
 
   // A helper function to handle _com_error result in DetectUpdatedRegion.
   // Returns false if the _com_error shows an error.
   static bool HandleDetectUpdatedRegionError(const _com_error& error,
                                              const char* stage);
 
   // Processes one frame received from AcquireNextFrame function, returns a
-  // nullptr if anything wrong, and Capture function will call
-  // callback_->OnCaptureCompleted(nullptr), otherwise
-  // callback_->OnCaptureCompleted(frame) will be called.
+  // nullptr if anything wrong.
   std::unique_ptr<DesktopFrame> ProcessFrame(
       const DXGI_OUTDUPL_FRAME_INFO& frame_info,
       IDXGIResource* resource);
 
   // A shortcut to execute callback with current frame in frames.
   void EmitCurrentFrame();
 
   ScreenCaptureFrameQueue<rtc::scoped_refptr<Texture>> surfaces_;
   ScreenCaptureFrameQueue<SharedDesktopFrame> frames_;
   std::unique_ptr<SharedMemoryFactory> shared_memory_factory_;
   Callback* callback_ = nullptr;
 
   bool set_thread_execution_state_failed_ = false;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(ScreenCapturerWinDirectx);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_WIN_SCREEN_CAPTURER_WIN_DIRECTX_H_