Adding ViE CallStats to keep track of call statistics. As a start, only rtt is handled.

This CL will be followed by another CL connecting the dots.

BUG=769
TEST=New unittest added.

Review URL: https://webrtc-codereview.appspot.com/968006

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@3117 4adac7df-926f-26a2-2b94-8c16560cd09d
5 files changed