Add the WebRTC.webkitApiCountPerSession metric.

content/renderer/media/rtc_peer_connection_handler.cc

Index: content/renderer/media/rtc_peer_connection_handler.cc
diff --git a/content/renderer/media/rtc_peer_connection_handler.cc b/content/renderer/media/rtc_peer_connection_handler.cc
index 167bdb88f3100df2381041bb42bf9171b64101e2..3b94de787da388c47c92b768072384bb71964d05 100644
--- a/content/renderer/media/rtc_peer_connection_handler.cc
+++ b/content/renderer/media/rtc_peer_connection_handler.cc
@@ -27,6 +27,7 @@
 #include "content/renderer/media/rtc_media_constraints.h"
 #include "content/renderer/media/webrtc_audio_capturer.h"
 #include "content/renderer/media/webrtc_audio_device_impl.h"
+#include "content/renderer/media/webrtc_uma_histograms.h"
 #include "content/renderer/render_thread_impl.h"
 #include "third_party/WebKit/public/platform/WebMediaConstraints.h"
 #include "third_party/WebKit/public/platform/WebMediaStreamSource.h"
@@ -553,6 +554,8 @@ bool RTCPeerConnectionHandler::addStream(
     peer_connection_tracker_->TrackAddStream(
         this, stream, PeerConnectionTracker::SOURCE_LOCAL);
 
+  PerSessionWebRTCAPIMetrics::GetInstance()->IncrementStreamCounter();
+
   track_metrics_.AddStream(MediaStreamTrackMetrics::SENT_STREAM,
                            MediaStream::GetAdapter(stream));
 
@@ -591,6 +594,7 @@ void RTCPeerConnectionHandler::removeStream(
   if (peer_connection_tracker_)
     peer_connection_tracker_->TrackRemoveStream(
         this, stream, PeerConnectionTracker::SOURCE_LOCAL);
+  PerSessionWebRTCAPIMetrics::GetInstance()->DecrementStreamCounter();
   track_metrics_.RemoveStream(MediaStreamTrackMetrics::SENT_STREAM,
                               MediaStream::GetAdapter(stream));
 }
@@ -767,6 +771,8 @@ void RTCPeerConnectionHandler::OnAddStream(
         this, remote_stream->webkit_stream(),
         PeerConnectionTracker::SOURCE_REMOTE);
 
+  PerSessionWebRTCAPIMetrics::GetInstance()->IncrementStreamCounter();
+
   track_metrics_.AddStream(MediaStreamTrackMetrics::RECEIVED_STREAM,
                            stream_interface);
 
@@ -784,6 +790,7 @@ void RTCPeerConnectionHandler::OnRemoveStream(
 
   track_metrics_.RemoveStream(MediaStreamTrackMetrics::RECEIVED_STREAM,
                               stream_interface);
+  PerSessionWebRTCAPIMetrics::GetInstance()->DecrementStreamCounter();
 
   scoped_ptr<RemoteMediaStreamImpl> remote_stream(it->second);
   const blink::WebMediaStream& webkit_stream = remote_stream->webkit_stream();