[GCM] Add connection/persistent store metric collection

google_apis/gcm/engine/mcs_client.cc

Index: google_apis/gcm/engine/mcs_client.cc
diff --git a/google_apis/gcm/engine/mcs_client.cc b/google_apis/gcm/engine/mcs_client.cc
index ca97348839a325dd3c94f5857863087a2152504e..b1811f0f67e418e98107d32d62a3f540c02f2419 100644
--- a/google_apis/gcm/engine/mcs_client.cc
+++ b/google_apis/gcm/engine/mcs_client.cc
@@ -6,6 +6,7 @@
 
 #include "base/basictypes.h"
 #include "base/message_loop/message_loop.h"
+#include "base/metrics/histogram.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/time/clock.h"
 #include "base/time/time.h"
@@ -346,6 +347,7 @@ void MCSClient::SendHeartbeat() {
 
 void MCSClient::OnRMQUpdateFinished(bool success) {
   LOG_IF(ERROR, !success) << "RMQ Update failed!";
+  UMA_HISTOGRAM_BOOLEAN("GCM.StoreUpdateSucceeded", success);
   // TODO(zea): Rebuild the store from scratch in case of persistence failure?
 }