Add histograms for WebRTC estimated bitrate and pacer bitrate.

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 b4f77cb3bd008baa95658385455fdfdc7b0609ab..1454f1917be2622e90fb4b9a3e855ed58de776d8 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -52861,6 +52861,24 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="WebRTC.Call.EstimatedSendBitrateInKbps" units="kbits/s">
+  <owner>holmer@chromium.org</owner>
+  <summary>
+    Average estimated send bitrate during a call, counted from first packet sent
+    until Call instance is destroyed. Only mesured for calls that are at least
+    10 seconds long.
+  </summary>
+</histogram>
+
+<histogram name="WebRTC.Call.PacerBitrateInKbps" units="kbits/s">
+  <owner>holmer@chromium.org</owner>
+  <summary>
+    Average pacer bitrate during a call, counted from first packet sent until
+    Call instance is destroyed. Only mesured for calls that are at least 10
+    seconds long.
+  </summary>
+</histogram>
+
 <histogram name="WebRTC.Call.RtcpBitrateReceivedInBps" units="bits/s">
   <owner>holmer@chromium.org</owner>
   <summary>