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

Source/core/html/shadow/SpinButtonElement.cpp

 /*
  * Copyright (C) 2006, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 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
@@ skipping 98 matching lines @@
                     doStepAction(m_upDownState == Up ? 1 : -1);
                 }
             }
             event->setDefaultHandled();
         }
     } else if (mouseEvent->type() == eventNames().mouseupEvent && mouseEvent->button() == LeftButton)
         stopRepeatingTimer();
     else if (event->type() == eventNames().mousemoveEvent) {
         if (box->pixelSnappedBorderBoxRect().contains(local)) {
             if (!m_capturing) {
-                if (Frame* frame = document()->frame()) {
+                if (Frame* frame = document().frame()) {
                     frame->eventHandler()->setCapturingMouseEventsNode(this);
                     m_capturing = true;
-                    if (Page* page = document()->page())
+                    if (Page* page = document().page())
                         page->chrome().registerPopupOpeningObserver(this);
                 }
             }
             UpDownState oldUpDownState = m_upDownState;
             m_upDownState = (local.y() < box->height() / 2) ? Up : Down;
             if (m_upDownState != oldUpDownState)
                 renderer()->repaint();
         } else {
             releaseCapture();
             m_upDownState = Indeterminate;
@@ skipping 52 matching lines @@
     if (amount > 0)
         m_spinButtonOwner->spinButtonStepUp();
     else if (amount < 0)
         m_spinButtonOwner->spinButtonStepDown();
 }
 
 void SpinButtonElement::releaseCapture()
 {
     stopRepeatingTimer();
     if (m_capturing) {
-        if (Frame* frame = document()->frame()) {
+        if (Frame* frame = document().frame()) {
             frame->eventHandler()->setCapturingMouseEventsNode(0);
             m_capturing = false;
-            if (Page* page = document()->page())
+            if (Page* page = document().page())
                 page->chrome().unregisterPopupOpeningObserver(this);
         }
     }
 }
 
 bool SpinButtonElement::matchesReadOnlyPseudoClass() const
 {
     return shadowHost()->matchesReadOnlyPseudoClass();
 }
 
@@ skipping 40 matching lines @@
         m_upDownState = Indeterminate;
     HTMLDivElement::setHovered(flag);
 }
 
 bool SpinButtonElement::shouldRespondToMouseEvents()
 {
     return !m_spinButtonOwner || m_spinButtonOwner->shouldSpinButtonRespondToMouseEvents();
 }
 
 }