Add a new UMA to GCM

This is used to find out the GCM usage from non-signed-in users.

BUG=384041
TEST=none

Review URL: https://codereview.chromium.org/605363002

Cr-Commit-Position: refs/heads/master@{#297045}

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"
@@ -645,6 +646,8 @@ 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(

tools/metrics/histograms/histograms.xml

@@ -9233,6 +9233,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>Number of retries before a GCM unregistration succeeds.</summary>
 </histogram>
 
+<histogram name="GCM.UserSignedIn" enum="Boolean">
+  <owner>jianli@chromium.org</owner>
+  <summary>
+    Indicates whether the user was signed in when GCM started up.
+  </summary>
+</histogram>
+
 <histogram name="GCMInvalidations.IncomingMessageStatus"
     enum="GCMInvalidationsIncomingMessageStatus">
   <owner>pavely@chromium.org</owner>