Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/plugins/DOMPluginArray.cpp

Index: Source/core/plugins/DOMPluginArray.cpp
diff --git a/Source/core/plugins/DOMPluginArray.cpp b/Source/core/plugins/DOMPluginArray.cpp
index d8659851f6cd79f5d8d61b7c204ac4b2e7cbfa67..7fb2686aa54f9ef5972a5295341dc31ec614f8db 100644
--- a/Source/core/plugins/DOMPluginArray.cpp
+++ b/Source/core/plugins/DOMPluginArray.cpp
@@ -51,10 +51,10 @@ PassRefPtrWillBeRawPtr<DOMPlugin> DOMPluginArray::item(unsigned index)
 {
     PluginData* data = pluginData();
     if (!data)
-        return 0;
+        return nullptr;
     const Vector<PluginInfo>& plugins = data->plugins();
     if (index >= plugins.size())
-        return 0;
+        return nullptr;
     return DOMPlugin::create(data, m_frame, index).get();
 }
 
@@ -75,13 +75,13 @@ PassRefPtrWillBeRawPtr<DOMPlugin> DOMPluginArray::namedItem(const AtomicString&
 {
     PluginData* data = pluginData();
     if (!data)
-        return 0;
+        return nullptr;
     const Vector<PluginInfo>& plugins = data->plugins();
     for (unsigned i = 0; i < plugins.size(); ++i) {
         if (plugins[i].name == propertyName)
             return DOMPlugin::create(data, m_frame, i).get();
     }
-    return 0;
+    return nullptr;
 }
 
 void DOMPluginArray::refresh(bool reload)