Add RTCPeerConnection RAPPOR metrics.

tools/metrics/rappor/rappor.xml

 <!--
 Copyright 2015 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.
 -->
 
 <rappor-configuration>
 <!--
 This file is used to generate a comprehensive list of Chrome rappor metrics
 along with a detailed description for each histogram. See the design doc at
@@ skipping 1623 matching lines @@
   </summary>
 </rappor-metric>
 
 <rappor-metric name="PushMessaging.MessageReceived.Origin" type="ETLD_PLUS_ONE">
   <owner>miguelg@chromium.org</owner>
   <summary>
     Push Messages received per Origin.
   </summary>
 </rappor-metric>
 
+<rappor-metric name="RTCPeerConnection.Connected" type="ETLD_PLUS_ONE">
+  <owner>guidou@chromium.org</owner>
+  <owner>hta@chromium.org</owner>
+  <owner>tommi@chromium.org</owner>
+  <summary>
+    The ETLD+1 of the URL with a WebRTC peer connection that has successfully
+    found a usable connection. Recorded when the ICE connection state of an
+    RTCPeerConnection object changes to connected.
+  </summary>
+</rappor-metric>
+
+<rappor-metric name="RTCPeerConnection.Created" type="ETLD_PLUS_ONE">
+  <owner>guidou@chromium.org</owner>
+  <owner>hta@chromium.org</owner>
+  <owner>tommi@chromium.org</owner>
+  <summary>
+    The ETLD+1 of the URL that created a WebRTC peer connection. Recorded when
+    an RTCPeerConnection object is created.
+  </summary>
+</rappor-metric>
+
+<rappor-metric name="RTCPeerConnection.Stable" type="ETLD_PLUS_ONE">

[Steven Holte, 2016/06/23 20:21:06]

It looks like these metrics will essentially be reporting the same value 3
times, which weakens the privacy value effect of the non-deterministic portion
of the noise.  It would be better if you rearranged the metrics so that they
report in a non-overlapping way, e.g. (created but not used), (connected but not
stable), (stable).

+  <owner>guidou@chromium.org</owner>
+  <owner>hta@chromium.org</owner>
+  <owner>tommi@chromium.org</owner>
+  <summary>
+    The ETLD+1 of the URL with a WebRTC peer connection that has completed an
+    offer/answer exchange. Recorded when the signaling state of an
+    RTCPeerConnection object changes to stable.
+  </summary>
+</rappor-metric>
+
 <rappor-metric name="ResourceReporter.Cpu" type="UMA_RAPPOR_TYPE">
   <owner>afakhry@chromium.org</owner>
   <summary>
     A Chrome task, its process priority, and its CPU usage range.
   </summary>
   <string-field name="task">
     <summary>
       The canonicalized name of a Chrome task. In most cases this is the origin
       URL of the task's WebContents.
     </summary>
@@ skipping 373 matching lines @@
     <flag>Bit 1: IS_REPEAT_VISIT</flag>
     <summary>
       Bitfield of the state from an SSL warning interstitial.
     </summary>
   </flags-field>
 </rappor-metric>
 
 </rappor-metrics>
 
 </rappor-configuration>