Clear CSSGlobalRuleSet on StyleEngine::didDetach().

third_party/WebKit/Source/core/css/CSSGlobalRuleSet.h

 // Copyright 2016 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 CSSGlobalRuleSet_h
 #define CSSGlobalRuleSet_h
 
 #include "core/css/RuleFeature.h"
 
 namespace blink {
@@ skipping 10 matching lines @@
 // to the ScopedStyleResolver as possible to avoid full reconstruction of these
 // rulesets on shadow tree changes. See https://crbug.com/401359
 
 class CSSGlobalRuleSet {
   DISALLOW_NEW();
   WTF_MAKE_NONCOPYABLE(CSSGlobalRuleSet);
 
  public:
   CSSGlobalRuleSet() {}
 
+  void dispose();
   void initWatchedSelectorsRuleSet(Document&);
   void markDirty() { m_isDirty = true; }
   bool isDirty() const { return m_isDirty; }
   void update(Document&);
 
   const RuleFeatureSet& ruleFeatureSet() const { return m_features; }
   RuleSet* siblingRuleSet() const { return m_siblingRuleSet; }
   RuleSet* uncommonAttributeRuleSet() const {
     return m_uncommonAttributeRuleSet;
   }
@@ skipping 12 matching lines @@
   // Rules injected from extensions.
   Member<RuleSet> m_watchedSelectorsRuleSet;
 
   bool m_hasFullscreenUAStyle = false;
   bool m_isDirty = true;
 };
 
 }  // namespace blink
 
 #endif  // CSSGlobalRuleSet_h