Race in StreamStatisticianImpl::GetStatistics vs. ::IncomingPacket

  StreamStatisticianImpl.ssrc_ is protected by stream_lock_, should
  be cached while holding lock to avoid race condition.

  Also, rtp_callback_ do not need to be called in GetStatistics() at all

BUG=2853
R=pbos@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/7619004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5435 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed