Refactor some receive-side stats.

Removes polling of CName as well as receive codec statistics in favor of
internal callbacks keeping a statistics struct up to date.

R=mflodman@webrtc.org, stefan@webrtc.org
BUG=1667

Review URL: https://webrtc-codereview.appspot.com/28259005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7950 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/rtp_rtcp/source/rtcp_receiver_unittest.cc

@@ -820,6 +820,8 @@ TEST_F(RtcpReceiverTest, Callbacks) {
       ssrc_ = ssrc;
     }
 
+    virtual void CNameChanged(const char* cname, uint32_t ssrc) OVERRIDE {}
+
     bool Matches(uint32_t ssrc, uint32_t extended_max, uint8_t fraction_loss,
                  uint32_t cumulative_loss, uint32_t jitter) {
       return ssrc_ == ssrc &&