Use C++11 features in core/html

Source/core/html/track/TextTrackCueList.cpp

 /*
  * Copyright (C) 2011 Google Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 31 matching lines @@
 
 unsigned long TextTrackCueList::getCueIndex(TextTrackCue* cue) const
 {
     return m_list.find(cue);
 }
 
 TextTrackCue* TextTrackCueList::item(unsigned index) const
 {
     if (index < m_list.size())
         return m_list[index].get();
-    return 0;
+    return nullptr;
 }
 
 TextTrackCue* TextTrackCueList::getCueById(const AtomicString& id) const
 {
     for (size_t i = 0; i < m_list.size(); ++i) {
         if (m_list[i]->id() == id)
             return m_list[i].get();
     }
-    return 0;
+    return nullptr;
 }
 
 TextTrackCueList* TextTrackCueList::activeCues()
 {
     if (!m_activeCues)
         m_activeCues = create();
 
     m_activeCues->clear();
     for (size_t i = 0; i < m_list.size(); ++i) {
         RefPtrWillBeRawPtr<TextTrackCue> cue = m_list[i];
@@ skipping 71 matching lines @@
         m_list[i]->invalidateCueIndex();
 }
 
 void TextTrackCueList::trace(Visitor* visitor)
 {
     visitor->trace(m_list);
     visitor->trace(m_activeCues);
 }
 
 } // namespace blink