Make GCMDriver::GetInstanceIDHandler protected, to avoid misuse

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 2c65b08eb09b54fe84e63d0eedbe34feb5dd19bb..171e4faf4d3ca7540a014736b8a4a0e76ebd498e 100644
--- a/components/gcm_driver/gcm_driver_desktop.cc
+++ b/components/gcm_driver/gcm_driver_desktop.cc
@@ -820,7 +820,7 @@ void GCMDriverDesktop::SetLastTokenFetchTime(const base::Time& time) {
                  time));
 }
 
-InstanceIDHandler* GCMDriverDesktop::GetInstanceIDHandler() {
+InstanceIDHandler* GCMDriverDesktop::GetInstanceIDHandlerInternal() {
   return this;
 }