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 72efdaf7b2c467c8c0375551eb97802cade840dc..3a91403c247cef360657191d4ff1bf323482c18d 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -37895,6 +37895,15 @@ 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 local Candidates gathered in a PeerConnection Session once
+    the ICE address gathering process reaches the Completed status. To avoid
+    miscounting, this only includes the first m line's first component.
+  </summary>
+</histogram>
+
 <histogram name="WebRTC.PeerConnection.IPv6Interfaces">
   <owner>mallinath@chromium.org</owner>
   <summary>
@@ -37902,6 +37911,15 @@ 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 local Candidates gathered in a PeerConnection Session once
+    the ICE address gathering process reaches the Completed status. To avoid
+    miscounting, this only includes the first m line's first component.
+  </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>