Add a new UMA to GCM

components/gcm_driver/gcm_driver_desktop.cc

Index: components/gcm_driver/gcm_driver_desktop.cc
diff --git a/components/gcm_driver/gcm_driver_desktop.cc b/components/gcm_driver/gcm_driver_desktop.cc
index b2d2e558c32c207b63bbd799f9d1fa1a4eb0d680..77e8f2b28e1ed1f1738f4ea6ae8678ad9f60e39c 100644
--- a/components/gcm_driver/gcm_driver_desktop.cc
+++ b/components/gcm_driver/gcm_driver_desktop.cc
@@ -11,6 +11,7 @@
 #include "base/files/file_path.h"
 #include "base/location.h"
 #include "base/logging.h"
+#include "base/metrics/histogram.h"
 #include "base/sequenced_task_runner.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "components/gcm_driver/gcm_app_handler.h"
@@ -649,6 +650,8 @@ GCMClient::Result GCMDriverDesktop::EnsureStarted() {
   if (GCMDriver::IsAllowedForAllUsers())
     gcm_channel_status_syncer_->EnsureStarted();
 
+  UMA_HISTOGRAM_BOOLEAN("GCM.UserSignedIn", signed_in_);
+
   // Note that we need to pass weak pointer again since the existing weak
   // pointer in IOWorker might have been invalidated when check-out occurs.
   io_thread_->PostTask(