Make GCMDriver::GetInstanceIDHandler protected, to avoid misuse

components/gcm_driver/gcm_driver_android.h

Index: components/gcm_driver/gcm_driver_android.h
diff --git a/components/gcm_driver/gcm_driver_android.h b/components/gcm_driver/gcm_driver_android.h
index dab0d149821ddc4736f23b5cc1405eef9ad45282..5944b85b1f3f7b3a648dfefbf14f557743ec74ce 100644
--- a/components/gcm_driver/gcm_driver_android.h
+++ b/components/gcm_driver/gcm_driver_android.h
@@ -74,7 +74,7 @@ class GCMDriverAndroid : public GCMDriver,
   base::Time GetLastTokenFetchTime() override;
   void SetLastTokenFetchTime(const base::Time& time) override;
   void WakeFromSuspendForHeartbeat(bool wake) override;
-  InstanceIDHandler* GetInstanceIDHandler() override;
+  InstanceIDHandler* GetInstanceIDHandlerInternal() override;
   void AddHeartbeatInterval(const std::string& scope, int interval_ms) override;
   void RemoveHeartbeatInterval(const std::string& scope) override;