Add CreateWindowCapturer() and CreateScreenCapturer() in DesktopCapturer

webrtc/modules/desktop_capture/desktop_capture.gypi

Index: webrtc/modules/desktop_capture/desktop_capture.gypi
diff --git a/webrtc/modules/desktop_capture/desktop_capture.gypi b/webrtc/modules/desktop_capture/desktop_capture.gypi
index ab1fd32f9fa024b8fc3940a1ea6ae0f415d8429d..b6d6f9992c029c883f93da98e56e0ba99347f8b2 100644
--- a/webrtc/modules/desktop_capture/desktop_capture.gypi
+++ b/webrtc/modules/desktop_capture/desktop_capture.gypi
@@ -141,6 +141,8 @@
         }],
         ['OS!="ios" ', {
           'sources': [
+            'desktop_capturer_differ_wrapper.cc',

[Sergey Ulanov, 2016/11/01 20:33:30]

Is gyp still being used somewhere?

[Hzj_jie, 2016/11/01 21:12:13]

No idea. Several trybots still have "gyp" in their names, but all of them are
dummy bots without really building the binary. Considering this file is still
existing, and referred by
https://cs.chromium.org/chromium/src/third_party/webrtc/modules/modules.gyp,
ensuring it buildable with this small effort looks safe.

+            'desktop_capturer_differ_wrapper.h',
             'differ_block.cc',
             'differ_block.h',
             'screen_capturer_differ_wrapper.cc',