Use FrameSelection::selectedText where possible.

third_party/WebKit/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 495 matching lines @@
 
     // This doesn't (and shouldn't) select text node characters.
     setBaseAndExtent(n, 0, n, n->countChildren(), exceptionState);
 }
 
 String DOMSelection::toString()
 {
     if (!m_frame)
         return String();
 
-    const EphemeralRange range = m_frame->selection().selection().toNormalizedEphemeralRange();
-    return plainText(range, TextIteratorForSelectionToString);
+    return m_frame->selection().selectedText(TextIteratorForSelectionToString);

[yosin_UTC9, 2015/10/06 05:41:51]

Since we can't change behavior Selection.toString() API at this time,
we should use DOM version of plainText().

Thus, we can't use |FrameSeleciton::selectedText()| here.
Once, we use DOM version, layout test failure will be gone.

 }
 
 Node* DOMSelection::shadowAdjustedNode(const Position& position) const
 {
     if (position.isNull())
         return 0;
 
     Node* containerNode = position.computeContainerNode();
     Node* adjustedNode = m_treeScope->ancestorInThisScope(containerNode);
 
@@ skipping 38 matching lines @@
         m_treeScope->document().addConsoleMessage(ConsoleMessage::create(JSMessageSource, ErrorMessageLevel, message));
 }
 
 DEFINE_TRACE(DOMSelection)
 {
     visitor->trace(m_treeScope);
     DOMWindowProperty::trace(visitor);
 }
 
 } // namespace blink