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

Source/core/rendering/RenderWidget.cpp

Index: Source/core/rendering/RenderWidget.cpp
diff --git a/Source/core/rendering/RenderWidget.cpp b/Source/core/rendering/RenderWidget.cpp
index f8572e6f9b0da6d31d3a21481b4895be559763bb..a4ea8ebb60e6ebd9e73d5d9628b169a1c757add4 100644
--- a/Source/core/rendering/RenderWidget.cpp
+++ b/Source/core/rendering/RenderWidget.cpp
@@ -83,7 +83,7 @@ static void moveWidgetToParentSoon(Widget* child, FrameView* parent)
 RenderWidget::RenderWidget(Element* element)
     : RenderReplaced(element)
     , m_widget(0)
-    , m_frameView(element->document()->view())
+    , m_frameView(element->document().view())
     // Reference counting is used to prevent the widget from being
     // destroyed while inside the Widget code, which might not be
     // able to handle that.
@@ -97,7 +97,7 @@ void RenderWidget::willBeDestroyed()
     if (RenderView* v = view())
         v->removeWidget(this);
 
-    if (AXObjectCache* cache = document()->existingAXObjectCache()) {
+    if (AXObjectCache* cache = document().existingAXObjectCache()) {
         cache->childrenChanged(this->parent());
         cache->remove(this);
     }
@@ -198,7 +198,7 @@ void RenderWidget::setWidget(PassRefPtr<Widget> widget)
         moveWidgetToParentSoon(m_widget.get(), m_frameView);
     }
 
-    if (AXObjectCache* cache = document()->existingAXObjectCache())
+    if (AXObjectCache* cache = document().existingAXObjectCache())
         cache->childrenChanged(this);
 }
 
@@ -296,7 +296,7 @@ void RenderWidget::paint(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
         paintInfo.context->restore();
 
     // Paint a partially transparent wash over selected widgets.
-    if (isSelected() && !document()->printing()) {
+    if (isSelected() && !document().printing()) {
         // FIXME: selectionRect() is in absolute, not painting coordinates.
         paintInfo.context->fillRect(pixelSnappedIntRect(selectionRect()), selectionBackgroundColor());
     }