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

Source/core/svg/SVGFitToViewBox.h

Index: Source/core/svg/SVGFitToViewBox.h
diff --git a/Source/core/svg/SVGFitToViewBox.h b/Source/core/svg/SVGFitToViewBox.h
index 736eca64083d696a3ba81b670eb6a51825267458..65284454aeac04cce24cae0bb8d7d90ced79857e 100644
--- a/Source/core/svg/SVGFitToViewBox.h
+++ b/Source/core/svg/SVGFitToViewBox.h
@@ -43,10 +43,9 @@ public:
     static bool parseAttribute(SVGElementTarget* target, const QualifiedName& name, const AtomicString& value)
     {
         ASSERT(target);
-        ASSERT(target->document());
         if (name == SVGNames::viewBoxAttr) {
             FloatRect viewBox;
-            bool valueIsValid = !value.isNull() && parseViewBox(target->document(), value, viewBox);
+            bool valueIsValid = !value.isNull() && parseViewBox(&target->document(), value, viewBox);
             target->setViewBoxBaseValue(viewBox, valueIsValid);
             return true;
         }