Add MouseCursorCapturer interface with implementation for X11.

The new interface will be used to capture cursor shape and position and
blend it into the image captured with desktop capturers.

BUG=crbug.com/173265
R=wez@chromium.org
TBR=andrew@webrtc.org (modules.gyp)

Review URL: https://webrtc-codereview.appspot.com/2386005

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@4967 4adac7df-926f-26a2-2b94-8c16560cd09d
14 files changed