Add two UMA counters for IPv4 and IPv6 local candidates gathered in WebRTC PeerConnection.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index f0257e013c070360fcffaa1c503d9b2df5189d8f..e43210ae1c59ddcf2cac9dc7125343e4c9e15c4d 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -37844,6 +37844,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="WebRTC.PeerConnection.IPv4LocalCandidates">
+  <owner>guoweis@chromium.org</owner>
+  <summary>
+    Number of IPv4 Candidates gathered in a PeerConnection Session.

[Alexei Svitkine (slow), 2014/09/25 15:10:52]

Please mention when this is logged, same for the one below.

+  </summary>
+</histogram>
+
 <histogram name="WebRTC.PeerConnection.IPv6Interfaces">
   <owner>mallinath@chromium.org</owner>
   <summary>
@@ -37851,6 +37858,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="WebRTC.PeerConnection.IPv6LocalCandidates">
+  <owner>guoweis@chromium.org</owner>
+  <summary>
+    Number of IPv6 Candidates gathered in a PeerConnection Session.
+  </summary>
+</histogram>
+
 <histogram name="WebRTC.PeerConnection.TimeToConnect" units="milliseconds">
   <owner>mallinath@chromium.org</owner>
   <summary>Time to setup a peer to peer call with PeerConnection.</summary>