The new DesktopCapturer interface will be used for screen and window captures. Beside DesktopCapturer itself also added classes/interfaces that it depends on. R=alexeypa@chromium.org, tommi@webrtc.org Review URL: https://webrtc-codereview.appspot.com/1322007 git-svn-id: http://webrtc.googlecode.com/svn/trunk@3917 4adac7df-926f-26a2-2b94-8c16560cd09d