Move VisibleSelection::ChangeObserver out from VisibleSelection class

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 1984 matching lines @@
 #endif
 
 DEFINE_TRACE(FrameSelection)
 {
     visitor->trace(m_frame);
     visitor->trace(m_selection);
     visitor->trace(m_originalBase);
     visitor->trace(m_logicalRange);
     visitor->trace(m_previousCaretNode);
     visitor->trace(m_typingStyle);
-    VisibleSelection::ChangeObserver::trace(visitor);
+    VisibleSelectionChangeObserver::trace(visitor);
 }
 
 void FrameSelection::setCaretRectNeedsUpdate()
 {
     m_caretRectDirty = true;
 
     scheduleVisualUpdate();
 }
 
 void FrameSelection::scheduleVisualUpdate() const
@@ skipping 75 matching lines @@
 
 void showTree(const blink::FrameSelection* sel)
 {
     if (sel)
         sel->showTreeForThis();
     else
         fprintf(stderr, "Cannot showTree for (nil) FrameSelection.\n");
 }
 
 #endif