Report metrics about negotiated ciphers.

talk/app/webrtc/peerconnectioninterface.h

Index: talk/app/webrtc/peerconnectioninterface.h
diff --git a/talk/app/webrtc/peerconnectioninterface.h b/talk/app/webrtc/peerconnectioninterface.h
index 3e4cb556fb5f51826734c719a5cf3f6e46bc36e8..d64775b66a6ef0c04ad2610a141b457b9aa1ef9b 100644
--- a/talk/app/webrtc/peerconnectioninterface.h
+++ b/talk/app/webrtc/peerconnectioninterface.h
@@ -127,6 +127,10 @@ class MetricsObserverInterface : public rtc::RefCountInterface {
   virtual void IncrementCounter(PeerConnectionMetricsCounter type) = 0;
   virtual void AddHistogramSample(PeerConnectionMetricsName type,
                                   int value) = 0;
+  // TODO(jbauch): Make method abstract when it is implemented by Chromium.
+  virtual void CiphersNegotiated(const std::string& content_name,

[juberti1, 2015/06/06 00:18:40]

This seems very ad-hoc. Can we abstract this into a general API where we can
specify the frequency of string values?

[joachim, 2015/06/08 20:58:40]

Are you thinking about something like
IncrementCounter(PeerConnectionMetricsKey type, const std::string& value);

where 'key' would be 'kPeerConnectionAudioSrtpCipher' or
'kPeerConnectionVideoSslCipher', etc. and 'value' the actual cipher suite?

+                                 const std::string& srtp_cipher,
+                                 const std::string& ssl_cipher) {};
 
  protected:
   virtual ~MetricsObserverInterface() {}