Node::setTextContent should avoid work when nothing changes

Source/core/editing/markup.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009, 2010, 2011 Google Inc. All rights reserved.
  * Copyright (C) 2011 Igalia S.L.
  * Copyright (C) 2011 Motorola Mobility. 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
@@ skipping 988 matching lines @@
     ASSERT(container);
     RefPtr<ContainerNode> containerNode(container);
 
     ChildListMutationScope mutation(*containerNode);
 
     if (!fragment->firstChild()) {
         containerNode->removeChildren();
         return;
     }
 
+    // FIXME: This is wrong if containerNode->firstChild() has more than one ref!

[Julien - ping for review, 2014/03/18 22:55:55]

I am not sure I understand this comment. All references should point to the same
Node or is it something else?

     if (containerNode->hasOneTextChild() && fragment->hasOneTextChild()) {
         toText(containerNode->firstChild())->setData(toText(fragment->firstChild())->data());
         return;
     }
 
+    // FIXME: No need to replace the child it is a text node and its contents are already == text.
     if (containerNode->hasOneChild()) {
         containerNode->replaceChild(fragment, containerNode->firstChild(), exceptionState);
         return;
     }
 
     containerNode->removeChildren();
     containerNode->appendChild(fragment, exceptionState);
 }
 
 void replaceChildrenWithText(ContainerNode* container, const String& text, ExceptionState& exceptionState)
 {
     ASSERT(container);
     RefPtr<ContainerNode> containerNode(container);
 
     ChildListMutationScope mutation(*containerNode);
 
+    // FIXME: This is wrong if containerNode->firstChild() has more than one ref!
     if (containerNode->hasOneTextChild()) {
         toText(containerNode->firstChild())->setData(text);
         return;
     }
 
+    // NOTE: This method currently always creates a text node, even if that text node will be empty.
     RefPtr<Text> textNode = Text::create(containerNode->document(), text);
 
+    // FIXME: No need to replace the child it is a text node and its contents are already == text.
     if (containerNode->hasOneChild()) {
         containerNode->replaceChild(textNode.release(), containerNode->firstChild(), exceptionState);
         return;
     }
 
     containerNode->removeChildren();
     containerNode->appendChild(textNode.release(), exceptionState);
 }
 
 void mergeWithNextTextNode(PassRefPtr<Node> node, ExceptionState& exceptionState)
 {
     ASSERT(node && node->isTextNode());
     Node* next = node->nextSibling();
     if (!next || !next->isTextNode())
         return;
 
     RefPtr<Text> textNode = toText(node.get());
     RefPtr<Text> textNext = toText(next);
     textNode->appendData(textNext->data());
     if (textNext->parentNode()) // Might have been removed by mutation event.
         textNext->remove(exceptionState);
 }
 
 }