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

Source/core/dom/MouseRelatedEvent.cpp

Index: Source/core/dom/MouseRelatedEvent.cpp
diff --git a/Source/core/dom/MouseRelatedEvent.cpp b/Source/core/dom/MouseRelatedEvent.cpp
index 14a40aacfeec8340688a4b05806c51e924e58604..147ba2dc73f1dc127a9fec3908f927261a9ebf2d 100644
--- a/Source/core/dom/MouseRelatedEvent.cpp
+++ b/Source/core/dom/MouseRelatedEvent.cpp
@@ -141,7 +141,7 @@ void MouseRelatedEvent::computeRelativePosition()
     m_offsetLocation = m_pageLocation;
 
     // Must have an updated render tree for this math to work correctly.
-    targetNode->document()->updateLayoutIgnorePendingStylesheets();
+    targetNode->document().updateLayoutIgnorePendingStylesheets();
 
     // Adjust offsetLocation to be relative to the target's position.
     if (RenderObject* r = targetNode->renderer()) {