Merge branch 'up-master'

Conflicts:
	browser/modules/webrtcUI.jsm
	content/media/webrtc/MediaEngine.h
	content/media/webrtc/MediaEngineWebRTC.cpp
	dom/media/MediaManager.cpp
	dom/webidl/MediaStreamTrack.webidl
	media/webrtc/trunk/webrtc/modules/desktop_capture/desktop_capture.gypi
	media/webrtc/trunk/webrtc/modules/desktop_capture/desktop_capture_types.h
	media/webrtc/trunk/webrtc/modules/desktop_capture/mouse_cursor_monitor_null.cc
	media/webrtc/trunk/webrtc/modules/desktop_capture/window_capturer_win.cc
	media/webrtc/trunk/webrtc/modules/desktop_capture/window_capturer_x11.cc
Merge branch 'master' into screenshare
Fix various build issues likely caused by the WebRTC 3.50 update.

Not sure if this is correct regarding the differences between ViEVideoFrameI420
and  I420VideoFrame, the constraints changes, and the logging.
make it compile and link
merge code with gcp's update