Move VisibleSelection::ChangeObserver out from VisibleSelection class

Source/core/editing/VisibleSelection.cpp

 /*
  * Copyright (C) 2004, 2005, 2006 Apple Computer, 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 1029 matching lines @@
 Element* VisibleSelection::rootEditableElement() const
 {
     return editableRootForPosition(start());
 }
 
 Node* VisibleSelection::nonBoundaryShadowTreeRootNode() const
 {
     return start().anchorNode() && !start().anchorNode()->isShadowRoot() ? start().anchorNode()->nonBoundaryShadowTreeRootNode() : 0;
 }
 
-VisibleSelection::ChangeObserver::ChangeObserver()
+VisibleSelectionChangeObserver::VisibleSelectionChangeObserver()
 {
 }
 
-VisibleSelection::ChangeObserver::~ChangeObserver()
+VisibleSelectionChangeObserver::~VisibleSelectionChangeObserver()
 {
 }
 
-void VisibleSelection::setChangeObserver(ChangeObserver& observer)
+void VisibleSelection::setChangeObserver(VisibleSelectionChangeObserver& observer)
 {
     ASSERT(!m_changeObserver);
     m_changeObserver = &observer;
 }
 
 void VisibleSelection::clearChangeObserver()
 {
     ASSERT(m_changeObserver);
     m_changeObserver = nullptr;
 }
@@ skipping 151 matching lines @@
     sel.showTreeForThis();
 }
 
 void showTree(const blink::VisibleSelection* sel)
 {
     if (sel)
         sel->showTreeForThis();
 }
 
 #endif