Update from https://crrev.com/327068

base/observer_list_threadsafe.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_OBSERVER_LIST_THREADSAFE_H_
 #define BASE_OBSERVER_LIST_THREADSAFE_H_
 
 #include <algorithm>
 #include <map>
 
@@ skipping 93 matching lines @@
   explicit ObserverListThreadSafe(NotificationType type) : type_(type) {}
 
   // Add an observer to the list.  An observer should not be added to
   // the same list more than once.
   void AddObserver(ObserverType* obs) {
     // If there is not a current MessageLoop, it is impossible to notify on it,
     // so do not add the observer.
     if (!base::MessageLoop::current())
       return;
 
-    ObserverList<ObserverType>* list = NULL;
+    ObserverList<ObserverType>* list = nullptr;
     base::PlatformThreadId thread_id = base::PlatformThread::CurrentId();
     {
       base::AutoLock lock(list_lock_);
       if (observer_lists_.find(thread_id) == observer_lists_.end())
         observer_lists_[thread_id] = new ObserverListContext(type_);
       list = &(observer_lists_[thread_id]->list);
     }
     list->AddObserver(obs);
   }
 
   // Remove an observer from the list if it is in the list.
   // If there are pending notifications in-transit to the observer, they will
   // be aborted.
   // If the observer to be removed is in the list, RemoveObserver MUST
   // be called from the same thread which called AddObserver.
   void RemoveObserver(ObserverType* obs) {
-    ObserverListContext* context = NULL;
-    ObserverList<ObserverType>* list = NULL;
+    ObserverListContext* context = nullptr;
+    ObserverList<ObserverType>* list = nullptr;
     base::PlatformThreadId thread_id = base::PlatformThread::CurrentId();
     {
       base::AutoLock lock(list_lock_);
       typename ObserversListMap::iterator it = observer_lists_.find(thread_id);
       if (it == observer_lists_.end()) {
         // This will happen if we try to remove an observer on a thread
         // we never added an observer for.
         return;
       }
       context = it->second;
@@ skipping 80 matching lines @@
       // have been removed and then re-added!  If the master list's loop
       // does not match this one, then we do not need to finish this
       // notification.
       if (it == observer_lists_.end() || it->second != context)
         return;
     }
 
     {
       typename ObserverList<ObserverType>::Iterator it(&context->list);
       ObserverType* obs;
-      while ((obs = it.GetNext()) != NULL)
+      while ((obs = it.GetNext()) != nullptr)
         method.Run(obs);
     }
 
     // If there are no more observers on the list, we can now delete it.
     if (context->list.size() == 0) {
       {
         base::AutoLock lock(list_lock_);
         // Remove |list| if it's not already removed.
         // This can happen if multiple observers got removed in a notification.
         // See http://crbug.com/55725.
@@ skipping 13 matching lines @@
       ObserversListMap;
 
   mutable base::Lock list_lock_;  // Protects the observer_lists_.
   ObserversListMap observer_lists_;
   const NotificationType type_;
 
   DISALLOW_COPY_AND_ASSIGN(ObserverListThreadSafe);
 };
 
 #endif  // BASE_OBSERVER_LIST_THREADSAFE_H_