Use C++11 features in core/html

Source/core/html/track/vtt/VTTRegionList.cpp

Index: Source/core/html/track/vtt/VTTRegionList.cpp
diff --git a/Source/core/html/track/vtt/VTTRegionList.cpp b/Source/core/html/track/vtt/VTTRegionList.cpp
index 3a046f451752389d07ade4e439d23f05d3f92a7c..3d195dd1ba28a54a1e268c1e912edbfd7d95ba21 100644
--- a/Source/core/html/track/vtt/VTTRegionList.cpp
+++ b/Source/core/html/track/vtt/VTTRegionList.cpp
@@ -42,20 +42,20 @@ VTTRegion* VTTRegionList::item(unsigned index) const
     if (index < m_list.size())
         return m_list[index].get();
 
-    return 0;
+    return nullptr;
 }
 
 VTTRegion* VTTRegionList::getRegionById(const String& id) const
 {
     if (id.isEmpty())
-        return 0;
+        return nullptr;
 
     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;
 }
 
 void VTTRegionList::add(PassRefPtrWillBeRawPtr<VTTRegion> region)