Fix selector namespace prefix resolution.

third_party/WebKit/Source/core/css/CSSPageRule.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * (C) 2002-2003 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2002, 2005, 2006, 2008, 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 52 matching lines @@
             text.append(' ');
             text.append(pageSpecification);
         }
     }
     return text.toString();
 }
 
 void CSSPageRule::setSelectorText(const String& selectorText)
 {
     CSSParserContext context(parserContext(), 0);
-    CSSSelectorList selectorList = CSSParser::parseSelector(context, selectorText);
+    CSSSelectorList selectorList = CSSParser::parseSelector(context, parentStyleSheet() ? parentStyleSheet()->contents() : nullptr, selectorText);
     if (!selectorList.isValid())
         return;
 
     CSSStyleSheet::RuleMutationScope mutationScope(this);
 
     m_pageRule->wrapperAdoptSelectorList(std::move(selectorList));
 }
 
 String CSSPageRule::cssText() const
 {
@@ skipping 17 matching lines @@
 }
 
 DEFINE_TRACE(CSSPageRule)
 {
     visitor->trace(m_pageRule);
     visitor->trace(m_propertiesCSSOMWrapper);
     CSSRule::trace(visitor);
 }
 
 } // namespace blink