Add RTCPeerConnection RAPPOR metrics.

tools/metrics/rappor/rappor.xml

Index: tools/metrics/rappor/rappor.xml
diff --git a/tools/metrics/rappor/rappor.xml b/tools/metrics/rappor/rappor.xml
index 0a7f95a32dc2d7fa6123e5edcdb5fb48e7472a02..d15ac36155bc9d993c9dd1cefc7cbb72e3e34ad8 100644
--- a/tools/metrics/rappor/rappor.xml
+++ b/tools/metrics/rappor/rappor.xml
@@ -1641,6 +1641,38 @@ now we are only interested in H264, VP8 and VP9.
   </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>