Have Node::document() return a reference instead of a pointer

Source/core/html/HTMLPlugInElement.cpp

Index: Source/core/html/HTMLPlugInElement.cpp
diff --git a/Source/core/html/HTMLPlugInElement.cpp b/Source/core/html/HTMLPlugInElement.cpp
index 8d23225bd2cbd82de07321d01d0839aab566fec0..c76ee71fe6ea5393ed1163e781b5bfa65d229e28 100644
--- a/Source/core/html/HTMLPlugInElement.cpp
+++ b/Source/core/html/HTMLPlugInElement.cpp
@@ -93,7 +93,7 @@ void HTMLPlugInElement::detach(const AttachContext& context)
     m_instance.clear();
 
     if (m_isCapturingMouseEvents) {
-        if (Frame* frame = document()->frame())
+        if (Frame* frame = document().frame())
             frame->eventHandler()->setCapturingMouseEventsNode(0);
         m_isCapturingMouseEvents = false;
     }
@@ -113,7 +113,7 @@ void HTMLPlugInElement::resetInstance()
 
 PassScriptInstance HTMLPlugInElement::getInstance()
 {
-    Frame* frame = document()->frame();
+    Frame* frame = document().frame();
     if (!frame)
         return 0;
 
@@ -211,13 +211,13 @@ void HTMLPlugInElement::defaultEventHandler(Event* event)
 
 RenderWidget* HTMLPlugInElement::renderWidgetForJSBindings() const
 {
-    document()->updateLayoutIgnorePendingStylesheets();
+    document().updateLayoutIgnorePendingStylesheets();
     return existingRenderWidget();
 }
 
 bool HTMLPlugInElement::isKeyboardFocusable() const
 {
-    if (!document()->page())
+    if (!document().page())
         return false;
 
     const PluginView* plugin = pluginWidget() && pluginWidget()->isPluginView() ? static_cast<const PluginView*>(pluginWidget()) : 0;
@@ -244,9 +244,9 @@ bool HTMLPlugInElement::rendererIsFocusable() const
 
 NPObject* HTMLPlugInElement::getNPObject()
 {
-    ASSERT(document()->frame());
+    ASSERT(document().frame());
     if (!m_NPObject)
-        m_NPObject = document()->frame()->script()->createScriptObjectForPluginElement(this);
+        m_NPObject = document().frame()->script()->createScriptObjectForPluginElement(this);
     return m_NPObject;
 }