Introduce LiteralSet

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 38673154a67f16684d3b44f5d599e697de86d8cd..46acd4472340be0c7e7b660da1a5d5d36f8820d7 100644
--- a/Source/core/dom/QualifiedName.h
+++ b/Source/core/dom/QualifiedName.h
@@ -123,6 +123,10 @@ inline bool operator!=(const AtomicString& a, const QualifiedName& q) { return a
 inline bool operator==(const QualifiedName& q, const AtomicString& a) { return a == q.localName(); }
 inline bool operator!=(const QualifiedName& q, const AtomicString& a) { return a != q.localName(); }
 
+// Useful with TableSet.
+bool lessThanByImplAddress(const QualifiedName* const&, const QualifiedName* const&);

[eseidel, 2013/05/22 00:40:14]

I think these probably belong as static class methods on QualifiedName.  Or
traits-style?  traits might be cleaner.  Up to you.  Free methods don't make
much sense to me though.

+bool lessThanByLocalNameImplAddress(const QualifiedName* const&, const QualifiedName* const&);
+
 inline unsigned hashComponents(const QualifiedNameComponents& buf)
 {
     return StringHasher::hashMemory<sizeof(QualifiedNameComponents)>(&buf);