Pre-bind the 'xml' prefix for serialization of XML fragments

Source/core/editing/MarkupAccumulator.cpp

Index: Source/core/editing/MarkupAccumulator.cpp
diff --git a/Source/core/editing/MarkupAccumulator.cpp b/Source/core/editing/MarkupAccumulator.cpp
index 8be6e8a1722c1264be70af5c7f672e29f3ff3306..7fbd2e9372152423523568558721b30274a2a51f 100644
--- a/Source/core/editing/MarkupAccumulator.cpp
+++ b/Source/core/editing/MarkupAccumulator.cpp
@@ -109,7 +109,15 @@ MarkupAccumulator::~MarkupAccumulator()
 
 String MarkupAccumulator::serializeNodes(Node& targetNode, EChildrenOnly childrenOnly, Vector<QualifiedName>* tagNamesToSkip)
 {
-    serializeNodesWithNamespaces(targetNode, childrenOnly, 0, tagNamesToSkip);
+    Namespaces* namespaces = 0;
+    Namespaces namespaceHash;
+    if (!targetNode.document().isHTMLDocument()) {
+        // Add pre-bound namespaces for XML fragments.
+        namespaceHash.set(xmlAtom.impl(), XMLNames::xmlNamespaceURI.impl());
+        namespaces = &namespaceHash;
+    }
+
+    serializeNodesWithNamespaces(targetNode, childrenOnly, namespaces, tagNamesToSkip);
     return m_markup.toString();
 }