setAttributeNode() does not properly normalize case.

Source/core/dom/QualifiedName.h

Index: Source/core/dom/QualifiedName.h
diff --git a/Source/core/dom/QualifiedName.h b/Source/core/dom/QualifiedName.h
index 355ceeb9c70c3f8cd99485020c8e3c4170a0fffb..b42f9e45cd28b8ecb28236df4a86cc0e25d37d3d 100644
--- a/Source/core/dom/QualifiedName.h
+++ b/Source/core/dom/QualifiedName.h
@@ -82,6 +82,8 @@ public:
 
     bool matches(const QualifiedName& other) const { return m_impl == other.m_impl || (localName() == other.localName() && namespaceURI() == other.namespaceURI()); }
 
+    bool matchesPossiblyIgnoringCase(const QualifiedName& other, bool shouldIgnoreCase) const { return m_impl == other.m_impl || (equalPossiblyIgnoringCase(localName(), other.localName(), shouldIgnoreCase) && namespaceURI() == other.namespaceURI()); }
+
     bool hasPrefix() const { return m_impl->m_prefix != nullAtom; }
     void setPrefix(const AtomicString& prefix) { *this = QualifiedName(prefix, localName(), namespaceURI()); }