[WebRTC] Add ScreenCapturerDifferWrapper to share Differ across ScreenCapturers

webrtc/modules/desktop_capture/desktop_capture.gypi

 # Copyright (c) 2013 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.
 
 {
   'targets': [
@@ skipping 40 matching lines @@
         "mac/window_list_utils.cc",
         "mac/window_list_utils.h",
         "mouse_cursor.cc",
         "mouse_cursor.h",
         "mouse_cursor_monitor.h",
         "mouse_cursor_monitor_mac.mm",
         "mouse_cursor_monitor_win.cc",
         "mouse_cursor_monitor_x11.cc",
         "screen_capture_frame_queue.h",
         "screen_capturer.h",
+        "screen_capturer_differ_wrapper.cc",
+        "screen_capturer_differ_wrapper.h",
         "screen_capturer_helper.cc",
         "screen_capturer_helper.h",
         "screen_capturer_mac.mm",
         "screen_capturer_win.cc",
         "screen_capturer_x11.cc",
         "shared_desktop_frame.cc",
         "shared_desktop_frame.h",
         "shared_memory.cc",
         "shared_memory.h",
         "win/cursor.cc",
@@ skipping 107 matching lines @@
               'xcode_settings': {
                 'OTHER_CFLAGS': [ '-msse2', ],
               },
             }],
           ],
         },
       ],  # targets
     }],
   ],
 }