Add some virtual and OVERRIDEs in webrtc/common_audio/

BUG=163
R=andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/1899004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@4473 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed