Remove usage of base::ObserverList<T>::Iter::GetNext() in //components/prefs.

components/prefs/pref_notifier_impl.cc

Index: components/prefs/pref_notifier_impl.cc
diff --git a/components/prefs/pref_notifier_impl.cc b/components/prefs/pref_notifier_impl.cc
index 48dd57c22d20eae537736bc4aee73bb2951b797e..a5e8e9846aeab3cb21d5d665a88ba06c441a5356 100644
--- a/components/prefs/pref_notifier_impl.cc
+++ b/components/prefs/pref_notifier_impl.cc
@@ -19,10 +19,8 @@ PrefNotifierImpl::~PrefNotifierImpl() {
 
   // Verify that there are no pref observers when we shut down.
   for (const auto& observer_list : pref_observers_) {
-    PrefObserverList::Iterator obs_iterator(observer_list.second.get());
-    if (obs_iterator.GetNext()) {
+    if (observer_list.second->begin() != observer_list.second->end())

[Pam (message me for reviews), 2016/10/14 20:35:26]

Why not observer_list.second->size() ?

[dcheng, 2016/10/14 20:38:40]

size() isn't exposed by ObserverList. Since ObserverList is thread-safe-ish,
allow reentrancy, and allows mutation of ObserverList while dispatching to
observers, it turns out to be a bit tricky to implement this in a performant
way.

Thus, this somewhat silly looking check.

       LOG(WARNING) << "Pref observer found at shutdown.";
-    }
   }
 
   // Same for initialization observers.