Increase VPMVideoDecimator's initial max_frame_rate_ to 60, which allow us potentially do 60fps.

BUG=
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/21499006

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6274 4adac7df-926f-26a2-2b94-8c16560cd09d