base: Stop passing a non-const ref to ObserverListBase::Iterator.

base/prefs/pref_notifier_impl.cc

Index: base/prefs/pref_notifier_impl.cc
diff --git a/base/prefs/pref_notifier_impl.cc b/base/prefs/pref_notifier_impl.cc
index 6bf960388677153105370d2f2a9b5e2c80e72a5c..7ae5fe679f80e3e54e6cef34a1141c16419431af 100644
--- a/base/prefs/pref_notifier_impl.cc
+++ b/base/prefs/pref_notifier_impl.cc
@@ -22,7 +22,7 @@ PrefNotifierImpl::~PrefNotifierImpl() {
   // Verify that there are no pref observers when we shut down.
   for (PrefObserverMap::iterator it = pref_observers_.begin();
        it != pref_observers_.end(); ++it) {
-    PrefObserverList::Iterator obs_iterator(*(it->second));
+    PrefObserverList::Iterator obs_iterator(it->second);
     if (obs_iterator.GetNext()) {
       LOG(WARNING) << "pref observer found at shutdown " << it->first;
     }