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

webrtc/modules/desktop_capture/desktop_frame_win.h

Index: webrtc/modules/desktop_capture/desktop_frame_win.h
diff --git a/webrtc/modules/desktop_capture/desktop_frame_win.h b/webrtc/modules/desktop_capture/desktop_frame_win.h
index 3513e14ffb7954884b9726563b930434103bbddd..e9a374b2fc57c34d9218323bd0403a6f2ca0ba95 100644
--- a/webrtc/modules/desktop_capture/desktop_frame_win.h
+++ b/webrtc/modules/desktop_capture/desktop_frame_win.h
@@ -26,9 +26,9 @@ namespace webrtc {
 class DesktopFrameWin : public DesktopFrame {
  public:
   virtual ~DesktopFrameWin();
-  static DesktopFrameWin* Create(DesktopSize size,
-                                 SharedMemoryFactory* shared_memory_factory,
-                                 HDC hdc);
+
+  static std::unique_ptr<DesktopFrameWin>
+  Create(DesktopSize size, SharedMemoryFactory* shared_memory_factory, HDC hdc);
 
   HBITMAP bitmap() { return bitmap_; }