Make GCMDriver::GetInstanceIDHandler protected, to avoid misuse

components/gcm_driver/instance_id/instance_id_driver.cc

Index: components/gcm_driver/instance_id/instance_id_driver.cc
diff --git a/components/gcm_driver/instance_id/instance_id_driver.cc b/components/gcm_driver/instance_id/instance_id_driver.cc
index 9ec01c46b39266d835cd4d58604207f07dc775c8..374be2244a51c26945eddc7c0807fe702c45b07d 100644
--- a/components/gcm_driver/instance_id/instance_id_driver.cc
+++ b/components/gcm_driver/instance_id/instance_id_driver.cc
@@ -6,6 +6,7 @@
 
 #include "base/metrics/field_trial.h"
 #include "build/build_config.h"
+#include "components/gcm_driver/gcm_driver.h"
 #include "components/gcm_driver/instance_id/instance_id.h"
 
 namespace instance_id {
@@ -41,7 +42,9 @@ InstanceID* InstanceIDDriver::GetInstanceID(const std::string& app_id) {
   if (iter != instance_id_map_.end())
     return iter->second.get();
 
-  scoped_ptr<InstanceID> instance_id = InstanceID::Create(app_id, gcm_driver_);
+  gcm::InstanceIDHandler* handler = gcm_driver_->GetInstanceIDHandlerInternal();
+
+  scoped_ptr<InstanceID> instance_id = InstanceID::Create(app_id, handler);
   InstanceID* instance_id_ptr = instance_id.get();
   instance_id_map_.insert(std::make_pair(app_id, std::move(instance_id)));
   return instance_id_ptr;