Selectors with unknown namespace prefixes should be dropped.

Source/core/css/parser/CSSSelectorParser.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CSSSelectorParser_h
 #define CSSSelectorParser_h
 
 #include "core/CoreExport.h"
 #include "core/css/parser/CSSParserSelector.h"
 #include "core/css/parser/CSSParserTokenRange.h"
@@ skipping 31 matching lines @@
     PassOwnPtr<CSSParserSelector> consumeId(CSSParserTokenRange&);
     PassOwnPtr<CSSParserSelector> consumeClass(CSSParserTokenRange&);
     PassOwnPtr<CSSParserSelector> consumePseudo(CSSParserTokenRange&);
     PassOwnPtr<CSSParserSelector> consumeAttribute(CSSParserTokenRange&);
 
     CSSSelector::Relation consumeCombinator(CSSParserTokenRange&);
     CSSSelector::Match consumeAttributeMatch(CSSParserTokenRange&);
     CSSSelector::AttributeMatchType consumeAttributeFlags(CSSParserTokenRange&);
 
     const AtomicString& defaultNamespace() const;
-    QualifiedName determineNameInNamespace(const AtomicString& prefix, const AtomicString& localName);
+    const AtomicString& determineNamespace(const AtomicString& prefix);
     void prependTypeSelectorIfNeeded(const AtomicString& namespacePrefix, const AtomicString& elementName, CSSParserSelector*);
     void rewriteSpecifiersWithElementNameForCustomPseudoElement(const QualifiedName& tag, CSSParserSelector*, bool tagIsImplicit);
     void rewriteSpecifiersWithElementNameForContentPseudoElement(const QualifiedName& tag, CSSParserSelector*, bool tagIsImplicit);
     static PassOwnPtr<CSSParserSelector> addSimpleSelectorToCompound(PassOwnPtr<CSSParserSelector> compoundSelector, PassOwnPtr<CSSParserSelector> simpleSelector);
 
     const CSSParserContext& m_context;
     RawPtrWillBeMember<StyleSheetContents> m_styleSheet; // FIXME: Should be const
 
     bool m_failedParsing;
 };
 
 } // namespace
 
 #endif // CSSSelectorParser_h