Don't emit a default namespace declaration if it's already the default

Source/core/editing/MarkupAccumulator.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009, 2010 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.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 204 matching lines @@
         result.append(quoteChar);
         return;
     }
 
     // FIXME: This does not fully match other browsers. Firefox percent-escapes non-ASCII characters for innerHTML.
     result.append(quoteChar);
     appendAttributeValue(result, resolvedURLString, false);
     result.append(quoteChar);
 }
 
-bool MarkupAccumulator::shouldAddNamespaceElement(const Element& element)
+bool MarkupAccumulator::shouldAddNamespaceElement(const Element& element, Namespaces& namespaces)
 {
     // Don't add namespace attribute if it is already defined for this elem.
     const AtomicString& prefix = element.prefix();
-    if (prefix.isEmpty())
-        return !element.hasAttribute(xmlnsAtom);
+    if (prefix.isEmpty()) {
+        if (element.hasAttribute(xmlnsAtom)) {
+            namespaces.set(emptyAtom.impl(), element.namespaceURI().impl());
+            return false;
+        }
+        return true;
+    }
 
     DEFINE_STATIC_LOCAL(String, xmlnsWithColon, ("xmlns:"));
     return !element.hasAttribute(xmlnsWithColon + prefix);
 }
 
 bool MarkupAccumulator::shouldAddNamespaceAttribute(const Attribute& attribute, Namespaces& namespaces)
 {
     // Don't add namespace attributes twice
     if (attribute.name() == XMLNSNames::xmlnsAttr) {
         namespaces.set(emptyAtom.impl(), attribute.value().impl());
@@ skipping 151 matching lines @@
 
 static String nodeNamePreservingCase(const Element& element)
 {
     return element.tagQName().toString();
 }
 
 void MarkupAccumulator::appendOpenTag(StringBuilder& result, const Element& element, Namespaces* namespaces)
 {
     result.append('<');
     result.append(nodeNamePreservingCase(element));
-    if (!element.document().isHTMLDocument() && namespaces && shouldAddNamespaceElement(element))
+    if (!element.document().isHTMLDocument() && namespaces && shouldAddNamespaceElement(element, *namespaces))
         appendNamespace(result, element.prefix(), element.namespaceURI(), *namespaces);
 }
 
 void MarkupAccumulator::appendCloseTag(StringBuilder& result, const Element& element)
 {
     if (shouldSelfClose(element)) {
         if (element.isHTMLElement())
             result.append(' '); // XHTML 1.0 <-> HTML compatibility.
         result.append('/');
     }
@@ skipping 116 matching lines @@
 {
     if (!node.isElementNode() || shouldSelfClose(node) || (!node.hasChildren() && elementCannotHaveEndTag(node)))
         return;
 
     result.appendLiteral("</");
     result.append(nodeNamePreservingCase(toElement(node)));
     result.append('>');
 }
 
 }