Remove differ from ScreenCapturer implementations

webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.h

Index: webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.h
diff --git a/webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.h b/webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.h
index d1b6395eac4d69cf369cc30111844e211119a717..8d298f62a872e9e0587db7757d0e96eaa6900ee6 100644
--- a/webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.h
+++ b/webrtc/modules/desktop_capture/win/screen_capturer_win_gdi.h
@@ -19,14 +19,11 @@
 
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/modules/desktop_capture/screen_capture_frame_queue.h"
-#include "webrtc/modules/desktop_capture/screen_capturer_helper.h"
 #include "webrtc/modules/desktop_capture/shared_desktop_frame.h"
 #include "webrtc/modules/desktop_capture/win/scoped_thread_desktop.h"
 
 namespace webrtc {
 
-class Differ;
-
 // ScreenCapturerWinGdi captures 32bit RGB using GDI.
 //
 // ScreenCapturerWinGdi is double-buffered as required by ScreenCapturer.
@@ -61,10 +58,6 @@ class ScreenCapturerWinGdi : public ScreenCapturer {
   ScreenId current_screen_id_ = kFullDesktopScreenId;
   std::wstring current_device_key_;
 
-  // A thread-safe list of invalid rectangles, and the size of the most
-  // recently captured screen.
-  ScreenCapturerHelper helper_;
-
   ScopedThreadDesktop desktop_;
 
   // GDI resources used for screen capture.
@@ -78,9 +71,6 @@ class ScreenCapturerWinGdi : public ScreenCapturer {
   // the primary display's top-left.
   DesktopRect desktop_dc_rect_;
 
-  // Class to calculate the difference between two screen bitmaps.
-  std::unique_ptr<Differ> differ_;
-
   HMODULE dwmapi_library_ = NULL;
   DwmEnableCompositionFunc composition_func_ = nullptr;