Node::setTextContent should avoid work when nothing changes

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 41 matching lines @@
 #include "core/dom/StaticNodeList.h"
 #include "core/dom/TemplateContentDocumentFragment.h"
 #include "core/dom/Text.h"
 #include "core/dom/TreeScopeAdopter.h"
 #include "core/dom/UserActionElementSet.h"
 #include "core/dom/WheelController.h"
 #include "core/dom/shadow/ElementShadow.h"
 #include "core/dom/shadow/InsertionPoint.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/editing/htmlediting.h"
+#include "core/editing/markup.h"
 #include "core/events/BeforeLoadEvent.h"
 #include "core/events/Event.h"
 #include "core/events/EventDispatchMediator.h"
 #include "core/events/EventDispatcher.h"
 #include "core/events/EventListener.h"
 #include "core/events/GestureEvent.h"
 #include "core/events/KeyboardEvent.h"
 #include "core/events/MouseEvent.h"
 #include "core/events/MutationEvent.h"
 #include "core/events/TextEvent.h"
@@ skipping 1418 matching lines @@
     switch (nodeType()) {
         case TEXT_NODE:
         case CDATA_SECTION_NODE:
         case COMMENT_NODE:
         case PROCESSING_INSTRUCTION_NODE:
             setNodeValue(text);
             return;
         case ELEMENT_NODE:
         case ATTRIBUTE_NODE:
         case DOCUMENT_FRAGMENT_NODE: {
+            // FIXME: Merge this logic into replaceChildrenWithText.
             RefPtr<ContainerNode> container = toContainerNode(this);
+            // No need to do anything if the text is identical.
+            if (container->hasOneTextChild() && toText(container->firstChild())->data() == text)
+                return;
             ChildListMutationScope mutation(*this);
             container->removeChildren();
+            // Note: This API will not insert empty text nodes:
+            // http://dom.spec.whatwg.org/#dom-node-textcontent
             if (!text.isEmpty())
                 container->appendChild(document().createTextNode(text), ASSERT_NO_EXCEPTION);
             return;
         }
         case DOCUMENT_NODE:
         case DOCUMENT_TYPE_NODE:
             // Do nothing.
             return;
     }
     ASSERT_NOT_REACHED();
@@ skipping 1022 matching lines @@
         node->showTreeForThis();
 }
 
 void showNodePath(const WebCore::Node* node)
 {
     if (node)
         node->showNodePathForThis();
 }
 
 #endif