Adding support for jointly estimating bandwidth using all streams from the same sending client.

- Broke out the bandwidth estimation from the RTP module.
- Added conversion between RTP and NTP time bases.
- Added unittests.

BUG=

Review URL: https://webrtc-codereview.appspot.com/784009

git-svn-id: http://webrtc.googlecode.com/svn/trunk@2798 4adac7df-926f-26a2-2b94-8c16560cd09d
40 files changed