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

Source/core/rendering/svg/RenderSVGResource.cpp

Index: Source/core/rendering/svg/RenderSVGResource.cpp
diff --git a/Source/core/rendering/svg/RenderSVGResource.cpp b/Source/core/rendering/svg/RenderSVGResource.cpp
index 6a2d951c96d2bf2f5c45886a38fce6d19757bb19..1b1bbe9e17fa6c37257c8cda7467ae10618cf348 100644
--- a/Source/core/rendering/svg/RenderSVGResource.cpp
+++ b/Source/core/rendering/svg/RenderSVGResource.cpp
@@ -174,7 +174,7 @@ static inline void removeFromCacheAndInvalidateDependencies(RenderObject* object
 
     if (!object->node() || !object->node()->isSVGElement())
         return;
-    HashSet<SVGElement*>* dependencies = object->document()->accessSVGExtensions()->setOfElementsReferencingTarget(toSVGElement(object->node()));
+    HashSet<SVGElement*>* dependencies = object->document().accessSVGExtensions()->setOfElementsReferencingTarget(toSVGElement(object->node()));
     if (!dependencies)
         return;
     HashSet<SVGElement*>::iterator end = dependencies->end();
@@ -187,7 +187,6 @@ static inline void removeFromCacheAndInvalidateDependencies(RenderObject* object
 void RenderSVGResource::markForLayoutAndParentResourceInvalidation(RenderObject* object, bool needsLayout)
 {
     ASSERT(object);
-    ASSERT(object->document());
     ASSERT(object->node());
 
     if (needsLayout)