Making TimeToConnect metric more robust

content/renderer/media/rtc_peer_connection_handler.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/rtc_peer_connection_handler.h"
 
 #include <string>
 #include <utility>
 #include <vector>
 
@@ skipping 1288 matching lines @@
     webrtc::PeerConnectionInterface::IceConnectionState new_state) {
   TRACE_EVENT0("webrtc", "RTCPeerConnectionHandler::OnIceConnectionChange");
   DCHECK(thread_checker_.CalledOnValidThread());
   if (new_state == webrtc::PeerConnectionInterface::kIceConnectionChecking) {
     ice_connection_checking_start_ = base::TimeTicks::Now();
   } else if (new_state ==
       webrtc::PeerConnectionInterface::kIceConnectionConnected) {
     // If the state becomes connected, send the time needed for PC to become
     // connected from checking to UMA. UMA data will help to know how much
     // time needed for PC to connect with remote peer.
+    if (ice_connection_checking_start_.is_null()) {
+      UMA_HISTOGRAM_MEDIUM_TIMES("WebRTC.PeerConnection.TimeToConnect",
+                                 base::TimeDelta());

[pthatcher2, 2015/06/01 23:02:15]

Can you put a comment explaining why it's correct that the value will be zero?

[guoweis_left_chromium, 2015/06/08 19:55:38]

Done.

+    } else {
     UMA_HISTOGRAM_MEDIUM_TIMES(
         "WebRTC.PeerConnection.TimeToConnect",
         base::TimeTicks::Now() - ice_connection_checking_start_);
+    }
   }
 
   track_metrics_.IceConnectionChange(new_state);
   blink::WebRTCPeerConnectionHandlerClient::ICEConnectionState state =
       GetWebKitIceConnectionState(new_state);
   if (peer_connection_tracker_)
     peer_connection_tracker_->TrackIceConnectionStateChange(this, state);
   if(client_)
     client_->didChangeICEConnectionState(state);
 }
@@ skipping 171 matching lines @@
     base::WaitableEvent event(false, false);
     thread->PostTask(FROM_HERE,
         base::Bind(&RunSynchronousClosure, closure,
                    base::Unretained(trace_event_name),
                    base::Unretained(&event)));
     event.Wait();
   }
 }
 
 }  // namespace content