Make GCMDriver::GetInstanceIDHandler protected, to avoid misuse

components/gcm_driver/gcm_driver_android.cc

Index: components/gcm_driver/gcm_driver_android.cc
diff --git a/components/gcm_driver/gcm_driver_android.cc b/components/gcm_driver/gcm_driver_android.cc
index 8f345423db36a62f0467c668aa4db8a0a0af4b12..7845bd9922cdda1cd9686681437aa3ce61de12a3 100644
--- a/components/gcm_driver/gcm_driver_android.cc
+++ b/components/gcm_driver/gcm_driver_android.cc
@@ -199,7 +199,7 @@ void GCMDriverAndroid::SetLastTokenFetchTime(const base::Time& time) {
 void GCMDriverAndroid::WakeFromSuspendForHeartbeat(bool wake) {
 }
 
-InstanceIDHandler* GCMDriverAndroid::GetInstanceIDHandler() {
+InstanceIDHandler* GCMDriverAndroid::GetInstanceIDHandlerInternal() {
   // Not supported for Android.
   return NULL;
 }