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

Source/core/page/DragController.cpp

 /*
  * Copyright (C) 2007, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 355 matching lines @@
         HTMLInputElement* elementAsFileInput = asFileInput(element);
         if (m_fileInputElementUnderMouse != elementAsFileInput) {
             if (m_fileInputElementUnderMouse)
                 m_fileInputElementUnderMouse->setCanReceiveDroppedFiles(false);
             m_fileInputElementUnderMouse = elementAsFileInput;
         }
 
         if (!m_fileInputElementUnderMouse)
             m_page->dragCaretController().setCaretPosition(m_documentUnderMouse->frame()->visiblePositionForPoint(point));
 
-        Frame* innerFrame = element->document()->frame();
+        Frame* innerFrame = element->document().frame();
         dragSession.operation = dragIsMove(innerFrame->selection(), dragData) ? DragOperationMove : DragOperationCopy;
         dragSession.mouseIsOverFileInput = m_fileInputElementUnderMouse;
         dragSession.numberOfItemsToBeAccepted = 0;
 
         unsigned numberOfFiles = dragData->numberOfFiles();
         if (m_fileInputElementUnderMouse) {
             if (m_fileInputElementUnderMouse->isDisabledFormControl())
                 dragSession.numberOfItemsToBeAccepted = 0;
             else if (m_fileInputElementUnderMouse->multiple())
                 dragSession.numberOfItemsToBeAccepted = numberOfFiles;
@@ skipping 127 matching lines @@
         String text = dragData->asPlainText(innerFrame.get());
         if (text.isEmpty() || !innerFrame->editor().shouldInsertText(text, range.get(), EditorInsertActionDropped)) {
             return false;
         }
 
         if (setSelectionToDragCaret(innerFrame.get(), dragCaret, range, point))
             applyCommand(ReplaceSelectionCommand::create(m_documentUnderMouse.get(), createFragmentFromText(range.get(), text),  ReplaceSelectionCommand::SelectReplacement | ReplaceSelectionCommand::MatchStyle | ReplaceSelectionCommand::PreventNesting));
     }
 
     if (rootEditableElement) {
-        if (Frame* frame = rootEditableElement->document()->frame())
+        if (Frame* frame = rootEditableElement->document().frame())
             frame->eventHandler()->updateDragStateAfterEditDragIfNeeded(rootEditableElement.get());
     }
 
     return true;
 }
 
 bool DragController::canProcessDrag(DragData* dragData)
 {
     ASSERT(dragData);
 
@@ skipping 387 matching lines @@
     return false;
 #endif
 }
 
 void DragController::cleanupAfterSystemDrag()
 {
 }
 
 } // namespace WebCore