Wrap ScreenCapturer with ScreenCapturerDifferWrapper

webrtc/modules/desktop_capture/desktop_capture_options.h

Index: webrtc/modules/desktop_capture/desktop_capture_options.h
diff --git a/webrtc/modules/desktop_capture/desktop_capture_options.h b/webrtc/modules/desktop_capture/desktop_capture_options.h
index 2aa3e5197c0b3672d08a9e9dbaf574e116d35906..0199e6d75b3f8993abc0a9d61bd715c0992beeca 100644
--- a/webrtc/modules/desktop_capture/desktop_capture_options.h
+++ b/webrtc/modules/desktop_capture/desktop_capture_options.h
@@ -72,6 +72,13 @@ class DesktopCaptureOptions {
     disable_effects_ = disable_effects;
   }
 
+  // Flag indicating that the capturer should use pixel-wise differ to detect
+  // accurate updated region.

[Sergey Ulanov, 2016/09/09 00:03:40]

This comment makes it sound like updated_region() will only contain pixels that
have changed, which is not true. Suggest rewording:

 // Flag that should be set if the consumer uses updated_region() 
 // and the capturer should try to provide correct updated_region()
 // for the frames it generates (e.g. by comparing each frame with 
 // the previous one).

+  bool accurate_updated_region() const { return accurate_updated_region_; }

[Sergey Ulanov, 2016/09/09 00:03:39]

I don't think 'accurate' is the word to use here. updated_region() is always an
approximation. 
Maybe detect_updated_region?

+  void set_accurate_updated_region(bool accurate_updated_region) {
+    accurate_updated_region_ = accurate_updated_region;
+  }
+
 #if defined(WEBRTC_WIN)
   bool allow_use_magnification_api() const {
     return allow_use_magnification_api_;
@@ -110,6 +117,7 @@ class DesktopCaptureOptions {
   bool use_update_notifications_ = true;
 #endif
   bool disable_effects_ = true;
+  bool accurate_updated_region_ = false;
 };
 
 }  // namespace webrtc