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

Source/core/accessibility/AccessibilityObject.cpp

Index: Source/core/accessibility/AccessibilityObject.cpp
diff --git a/Source/core/accessibility/AccessibilityObject.cpp b/Source/core/accessibility/AccessibilityObject.cpp
index e474e0fe49d4c41b882d45540c39bab4a1513fc4..cec8980b3c1549f065798fdf1b63e4d80c2ad121 100644
--- a/Source/core/accessibility/AccessibilityObject.cpp
+++ b/Source/core/accessibility/AccessibilityObject.cpp
@@ -505,7 +505,7 @@ AccessibilityObject* AccessibilityObject::firstAccessibleObjectFromNode(const No
     if (!node)
         return 0;
 
-    AXObjectCache* cache = node->document()->axObjectCache();
+    AXObjectCache* cache = node->document().axObjectCache();
     AccessibilityObject* accessibleObject = cache->getOrCreate(node->renderer());
     while (accessibleObject && accessibleObject->accessibilityIsIgnored()) {
         node = NodeTraversal::next(node);
@@ -883,7 +883,7 @@ static bool replacedNodeNeedsCharacter(Node* replacedNode)
         return false;
 
     // create an AX object, but skip it if it is not supposed to be seen
-    AccessibilityObject* object = replacedNode->renderer()->document()->axObjectCache()->getOrCreate(replacedNode);
+    AccessibilityObject* object = replacedNode->renderer()->document().axObjectCache()->getOrCreate(replacedNode);
     if (object->accessibilityIsIgnored())
         return false;