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

Source/core/page/PrintContext.cpp

Index: Source/core/page/PrintContext.cpp
diff --git a/Source/core/page/PrintContext.cpp b/Source/core/page/PrintContext.cpp
index a8c284079f400d914a25f1dc2edc710dc8c8cbcd..0803a419c2df806d5206973287e1021cbc2e82d2 100644
--- a/Source/core/page/PrintContext.cpp
+++ b/Source/core/page/PrintContext.cpp
@@ -239,13 +239,13 @@ int PrintContext::pageNumberForElement(Element* element, const FloatSize& pageSi
 {
     // Make sure the element is not freed during the layout.
     RefPtr<Element> elementRef(element);
-    element->document()->updateLayout();
+    element->document().updateLayout();
 
     RenderBoxModelObject* box = enclosingBoxModelObject(element->renderer());
     if (!box)
         return -1;
 
-    Frame* frame = element->document()->frame();
+    Frame* frame = element->document().frame();
     FloatRect pageRect(FloatPoint(0, 0), pageSizeInPixels);
     PrintContext printContext(frame);
     printContext.begin(pageRect.width(), pageRect.height());
@@ -274,12 +274,12 @@ void PrintContext::collectLinkedDestinations(Node* node)
     const AtomicString& href = toElement(node)->getAttribute(HTMLNames::hrefAttr);
     if (href.isNull())
         return;
-    KURL url = node->document()->completeURL(href);
+    KURL url = node->document().completeURL(href);
     if (!url.isValid())
         return;
-    if (url.hasFragmentIdentifier() && equalIgnoringFragmentIdentifier(url, node->document()->baseURL())) {
+    if (url.hasFragmentIdentifier() && equalIgnoringFragmentIdentifier(url, node->document().baseURL())) {
         String name = url.fragmentIdentifier();
-        Element* element = node->document()->findAnchor(name);
+        Element* element = node->document().findAnchor(name);
         if (element)
             m_linkedDestinations.set(name, element);
     }