Record latencies of connection and arrival of first message in UMA

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 9e9ab5029ee24a38c9d269b874ca1afcec36b003..5dad61f48776b7f5114b735233c4732393b2834a 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8380,6 +8380,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>Net error results from GCM connection attempts.</summary>
 </histogram>
 
+<histogram name="GCM.ConnectionLatency" units="milliseconds">
+  <owner>juyik@chromium.org</owner>
+  <summary>
+    The time between the initiation of a connection and the successful
+    completion of it.
+  </summary>
+</histogram>
+
 <histogram name="GCM.ConnectionResetReason" enum="GCMConnectionResetReason">
   <owner>zea@chromium.org</owner>
   <summary>Reasons for GCM connection resets.</summary>
@@ -8401,6 +8409,22 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="GCM.DataMessageBurstReceivedInterval" units="milliseconds">
+  <owner>juyik@chromium.org</owner>
+  <summary>
+    Interval between two successive received data message bursts.
+  </summary>
+</histogram>
+
+<histogram name="GCM.FirstReceivedDataMessageLatencyAfterConnection"
+    units="milliseconds">
+  <owner>juyik@chromium.org</owner>
+  <summary>
+    The time between the successful completion of the connection and the arrival
+    of the first data message.
+  </summary>
+</histogram>
+
 <histogram name="GCM.LoadSucceeded" enum="BooleanSuccess">
   <owner>zea@chromium.org</owner>
   <summary>
@@ -8435,6 +8459,19 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="GCM.ReceivedDataMessageBurstSize" units="messages">
+  <owner>juyik@chromium.org</owner>
+  <summary>Number of messages in a received GCM data message burst.</summary>
+</histogram>
+
+<histogram name="GCM.ReceivedDataMessageIntervalWithinBurstMs"
+    units="milliseconds">
+  <owner>juyik@chromium.org</owner>
+  <summary>
+    Interval between messages within a received GCM data message burst.
+  </summary>
+</histogram>
+
 <histogram name="GCM.RegistrationCompleteTime" units="milliseconds">
   <owner>jianli@chromium.org</owner>
   <summary>