Introduce use counters for shadow DOM handling in plainText()

Source/core/editing/DOMSelection.cpp

 /*
  * Copyright (C) 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Google 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.
@@ skipping 487 matching lines @@
     setBaseAndExtent(n, 0, n, n->countChildren(), exceptionState);
 }
 
 String DOMSelection::toString()
 {
     if (!m_frame)
         return String();
 
     Position start, end;
     if (m_frame->selection().selection().toNormalizedPositions(start, end))
-        return plainText(start, end);
+        return plainText(start, end, TextIteratorForSelectionToString);
     return emptyString();
 }
 
 Node* DOMSelection::shadowAdjustedNode(const Position& position) const
 {
     if (position.isNull())
         return 0;
 
     Node* containerNode = position.containerNode();
     Node* adjustedNode = m_treeScope->ancestorInThisScope(containerNode);
@@ skipping 39 matching lines @@
         m_treeScope->document().addConsoleMessage(ConsoleMessage::create(JSMessageSource, ErrorMessageLevel, message));
 }
 
 DEFINE_TRACE(DOMSelection)
 {
     visitor->trace(m_treeScope);
     DOMWindowProperty::trace(visitor);
 }
 
 } // namespace blink