Have Frame::tree() return a reference

Source/core/editing/FrameSelection.cpp

 /*
  * Copyright (C) 2004, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1324 matching lines @@
 }
 
 // Workaround for the fact that it's hard to delete a frame.
 // Call this after doing user-triggered selections to make it easy to delete the frame you entirely selected.
 // Can't do this implicitly as part of every setSelection call because in some contexts it might not be good
 // for the focus to move to another frame. So instead we call it from places where we are selecting with the
 // mouse or the keyboard after setting the selection.
 void FrameSelection::selectFrameElementInParentIfFullySelected()
 {
     // Find the parent frame; if there is none, then we have nothing to do.
-    Frame* parent = m_frame->tree()->parent();
+    Frame* parent = m_frame->tree().parent();
     if (!parent)
         return;
     Page* page = m_frame->page();
     if (!page)
         return;
 
     // Check if the selection contains the entire frame contents; if not, then there is nothing to do.
     if (!isRange())
         return;
     if (!isStartOfDocument(selection().visibleStart()))
@@ skipping 510 matching lines @@
     sel.showTreeForThis();
 }
 
 void showTree(const WebCore::FrameSelection* sel)
 {
     if (sel)
         sel->showTreeForThis();
 }
 
 #endif