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

Source/core/html/shadow/HTMLShadowElement.cpp

Index: Source/core/html/shadow/HTMLShadowElement.cpp
diff --git a/Source/core/html/shadow/HTMLShadowElement.cpp b/Source/core/html/shadow/HTMLShadowElement.cpp
index d8b857db5b2cd2d246e0c92e0ee6ef4cff1ba869..1e2aa45d3855c7ede80743237722585a348bdcfa 100644
--- a/Source/core/html/shadow/HTMLShadowElement.cpp
+++ b/Source/core/html/shadow/HTMLShadowElement.cpp
@@ -60,7 +60,7 @@ ShadowRoot* HTMLShadowElement::olderShadowRoot()
     if (!containingRoot)
         return 0;
 
-    document()->updateDistributionForNodeIfNeeded(this);
+    document().updateDistributionForNodeIfNeeded(this);
 
     ShadowRoot* older = containingRoot->olderShadowRoot();
     if (!older || !older->shouldExposeToBindings() || older->insertionPoint() != this)
@@ -77,7 +77,7 @@ Node::InsertionNotificationRequest HTMLShadowElement::insertedInto(ContainerNode
         ShadowRoot* root = containingShadowRoot();
         if (root && root->olderShadowRoot() && root->type() != root->olderShadowRoot()->type()) {
             String message = String::format("<shadow> doesn't work for %s element host.", root->host()->tagName().utf8().data());
-            document()->addConsoleMessage(RenderingMessageSource, WarningMessageLevel, message);
+            document().addConsoleMessage(RenderingMessageSource, WarningMessageLevel, message);
         }
     }
     return InsertionPoint::insertedInto(insertionPoint);