Disable MouseCursorMonitorTest.FromScreen

The test is flaky.

BUG=3245
TBR=sergeyu@chromium.org

Review URL: https://webrtc-codereview.appspot.com/21579004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6300 4adac7df-926f-26a2-2b94-8c16560cd09d