Support for CSSOM CSSNamespaceRule interface

Source/core/css/CSSGroupingRule.cpp

 /*
  * Copyright (C) 2011 Adobe Systems Incorporated. All rights reserved.
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
@@ skipping 53 matching lines @@
     ASSERT(m_childRuleCSSOMWrappers.size() == m_groupRule->childRules().size());
 
     if (index > m_groupRule->childRules().size()) {
         exceptionState.throwDOMException(IndexSizeError, "the index " + String::number(index) + " must be less than or equal to the length of the rule list.");
         return 0;
     }
 
     CSSStyleSheet* styleSheet = parentStyleSheet();
     CSSParserContext context(parserContext(), UseCounter::getFrom(styleSheet));
     RefPtrWillBeRawPtr<StyleRuleBase> newRule = CSSParser::parseRule(context, styleSheet ? styleSheet->contents() : nullptr, ruleString);
-    // FIXME: @namespace rules have special handling in the CSSOM spec, but it
-    // mostly doesn't make sense since we don't support CSSNamespaceRule
-    if (!newRule || newRule->isNamespaceRule()) {
+    if (!newRule) {
         exceptionState.throwDOMException(SyntaxError, "the rule '" + ruleString + "' is invalid and cannot be parsed.");
         return 0;
     }
 
+    if (newRule->isNamespaceRule()) {
+        exceptionState.throwDOMException(HierarchyRequestError, "'@namespace' rules cannot be inserted inside a group rule.");
+        return 0;
+    }
+
     if (newRule->isImportRule()) {
         // FIXME: an HierarchyRequestError should also be thrown for a nested @media rule. They are
         // currently not getting parsed, resulting in a SyntaxError to get raised above.
         exceptionState.throwDOMException(HierarchyRequestError, "'@import' rules cannot be inserted inside a group rule.");
         return 0;
     }
     CSSStyleSheet::RuleMutationScope mutationScope(this);
 
     m_groupRule->wrapperInsertRule(index, newRule);
 
@@ skipping 66 matching lines @@
 {
     CSSRule::trace(visitor);
 #if ENABLE(OILPAN)
     visitor->trace(m_childRuleCSSOMWrappers);
 #endif
     visitor->trace(m_groupRule);
     visitor->trace(m_ruleListCSSOMWrapper);
 }
 
 } // namespace blink