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

Source/core/rendering/ImageQualityController.cpp

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 91 matching lines @@
     }
 }
 
 void ImageQualityController::highQualityRepaintTimerFired(Timer<ImageQualityController>*)
 {
     if (!m_animatedResizeIsActive && !m_liveResizeOptimizationIsActive)
         return;
     m_animatedResizeIsActive = false;
 
     for (ObjectLayerSizeMap::iterator it = m_objectLayerSizeMap.begin(); it != m_objectLayerSizeMap.end(); ++it) {
-        if (Frame* frame = it->key->document()->frame()) {
+        if (Frame* frame = it->key->document().frame()) {
             // If this renderer's containing FrameView is in live resize, punt the timer and hold back for now.
             if (frame->view() && frame->view()->inLiveResize()) {
                 restartTimer();
                 return;
             }
         }
         it->key->repaint();
     }
 
     m_liveResizeOptimizationIsActive = false;
@@ skipping 29 matching lines @@
 
     const AffineTransform& currentTransform = context->getCTM();
     bool contextIsScaled = !currentTransform.isIdentityOrTranslationOrFlipped();
 
     // Make sure to use the unzoomed image size, since if a full page zoom is in effect, the image
     // is actually being scaled.
     LayoutSize scaledImageSize = currentTransform.mapSize(image->size());
     LayoutSize scaledLayoutSize = currentTransform.mapSize(roundedIntSize(layoutSize));
 
     // If the containing FrameView is being resized, paint at low quality until resizing is finished.
-    if (Frame* frame = object->document()->frame()) {
+    if (Frame* frame = object->document().frame()) {
         bool frameViewIsCurrentlyInLiveResize = frame->view() && frame->view()->inLiveResize();
         if (frameViewIsCurrentlyInLiveResize) {
             set(object, innerMap, layer, scaledLayoutSize);
             restartTimer();
             m_liveResizeOptimizationIsActive = true;
             return true;
         }
         if (m_liveResizeOptimizationIsActive) {
             // Live resize has ended, paint in HQ and remove this object from the list.
             removeLayer(object, innerMap, layer);
@@ skipping 30 matching lines @@
     // This object has been resized to two different sizes while the timer
     // is active, so draw at low quality, set the flag for animated resizes and
     // the object to the list for high quality redraw.
     set(object, innerMap, layer, scaledLayoutSize);
     m_animatedResizeIsActive = true;
     restartTimer();
     return true;
 }
 
 } // namespace WebCore