[GCM] Move registration info persistence from extension state store to GCM store

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 13febe87bdd144ee592cdb25a190e88e32c5e546..1f545859c5ea6d20c5718a15472658fc25be6bbe 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -6600,13 +6600,6 @@ other types of suffix sets.
   </summary>
 </histogram>
 
-<histogram name="GCM.NumUsers">

[Alexei Svitkine (slow), 2014/03/21 15:41:37]

Please don't remove existing histograms. Instead, mark them as obsolete (check
the file for other examples).

[jianli, 2014/03/21 16:54:31]

Done.

-  <owner>zea@chromium.org</owner>
-  <summary>
-    Number of GCM users associated with this client at startup time.
-  </summary>
-</histogram>
-
 <histogram name="GCM.RegistrationRequestStatus"
     enum="GCMRegistrationRequestStatus">
   <owner>juyik@chromium.org</owner>
@@ -6629,6 +6622,13 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="GCM.RestoredRegistrations">
+  <owner>jianli@chromium.org</owner>
+  <summary>
+    Number of registrations restored from the persistent store at startup.
+  </summary>
+</histogram>
+
 <histogram name="GCM.StoreDestroySucceeded" enum="BooleanSuccess">
   <owner>zea@chromium.org</owner>
   <summary>