reset VisibleSelection at the Undo command.

Source/core/dom/Node.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 2540 matching lines @@
 {
     visitor->trace(m_parentOrShadowHostNode);
     visitor->trace(m_previous);
     visitor->trace(m_next);
     if (hasRareData())
         visitor->trace(rareData());
     visitor->trace(m_treeScope);
     EventTarget::trace(visitor);
 }
 
+unsigned Node::lengthOfContents() const
+{
+    // This switch statement must be consistent with that of Range::processContentsBetweenOffsets.
+    switch (nodeType()) {
+    case Node::TEXT_NODE:
+    case Node::CDATA_SECTION_NODE:
+    case Node::COMMENT_NODE:
+        return toCharacterData(this)->length();
+    case Node::PROCESSING_INSTRUCTION_NODE:
+        return toProcessingInstruction(this)->data().length();
+    case Node::ELEMENT_NODE:
+    case Node::ATTRIBUTE_NODE:
+    case Node::DOCUMENT_NODE:
+    case Node::DOCUMENT_FRAGMENT_NODE:
+        return toContainerNode(this)->countChildren();
+    case Node::DOCUMENT_TYPE_NODE:
+        return 0;
+    }
+    ASSERT_NOT_REACHED();
+    return 0;
+}
+
 } // namespace WebCore
 
 #ifndef NDEBUG
 
 void showNode(const WebCore::Node* node)
 {
     if (node)
         node->showNode("");
 }
 
 void showTree(const WebCore::Node* node)
 {
     if (node)
         node->showTreeForThis();
 }
 
 void showNodePath(const WebCore::Node* node)
 {
     if (node)
         node->showNodePathForThis();
 }
 
 #endif