[GCM] Update ResetStore histograms

components/gcm_driver/gcm_client_impl.h

Index: components/gcm_driver/gcm_client_impl.h
diff --git a/components/gcm_driver/gcm_client_impl.h b/components/gcm_driver/gcm_client_impl.h
index dcda57db288946f2086be305cbdbe23ce51c5969..edb637a7e0e8c0ac0c0501bfd59bdade3b8bb7a8 100644
--- a/components/gcm_driver/gcm_client_impl.h
+++ b/components/gcm_driver/gcm_client_impl.h
@@ -175,6 +175,16 @@ class GCMClientImpl
     std::set<std::string> last_checkin_accounts;
   };
 
+  // Reasons for resetting the GCM Store.
+  // Note: this enum is recorded into a histogram. Do not change enum value
+  // or order.
+  enum ResetReason {
+    LOAD_FAILURE,      // GCM store failed to load, but the store exists.
+    CHECKIN_REJECTED,  // Checkin was rejected by server.
+
+    RESET_REASON_COUNT,
+  };
+
   // Collection of pending registration requests. Keys are RegistrationInfo
   // instance, while values are pending registration requests to obtain a
   // registration ID for requesting application.