Add desktop_capture directory for screen and window capturers.

The screen captures will be moved from chromium to WebRTC to make it easy
to share this code with other projects. This CL adds a new directory where
the current screen capturer code will be moved to.

Review URL: https://webrtc-codereview.appspot.com/1297005

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@3866 4adac7df-926f-26a2-2b94-8c16560cd09d
3 files changed