Avoid always style recalc when removing stylesheets.

Source/core/css/CSSStyleSheet.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2008, 2009, 2010, 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 23 matching lines @@
 class CSSRule;
 class CSSRuleList;
 class CSSStyleSheet;
 class CSSStyleSheetResource;
 class Document;
 class ExceptionState;
 class MediaQuerySet;
 class SecurityOrigin;
 class StyleSheetContents;
 
+enum StyleSheetUpdateType {
+    PartialRuleUpdate,
+    EntireStyleSheetUpdate
+};
+
 class CSSStyleSheet : public StyleSheet {
 public:
     static PassRefPtr<CSSStyleSheet> create(PassRefPtr<StyleSheetContents>, CSSImportRule* ownerRule = 0);
     static PassRefPtr<CSSStyleSheet> create(PassRefPtr<StyleSheetContents>, Node* ownerNode);
     static PassRefPtr<CSSStyleSheet> createInline(Node*, const KURL&, const TextPosition& startPosition = TextPosition::minimumPosition(), const String& encoding = String());
 
     virtual ~CSSStyleSheet();
 
     virtual CSSStyleSheet* parentStyleSheet() const OVERRIDE;
     virtual Node* ownerNode() const OVERRIDE { return m_ownerNode; }
@@ skipping 10 matching lines @@
     // IE Extensions
     PassRefPtr<CSSRuleList> rules();
     int addRule(const String& selector, const String& style, int index, ExceptionState&);
     int addRule(const String& selector, const String& style, ExceptionState&);
     void removeRule(unsigned index, ExceptionState& es) { deleteRule(index, es); }
 
     // For CSSRuleList.
     unsigned length() const;
     CSSRule* item(unsigned index);
 
-    virtual void clearOwnerNode() OVERRIDE { didMutate(); m_ownerNode = 0; }
+    virtual void clearOwnerNode() OVERRIDE { didMutate(EntireStyleSheetUpdate); m_ownerNode = 0; }
     virtual CSSRule* ownerRule() const OVERRIDE { return m_ownerRule; }
     virtual KURL baseURL() const OVERRIDE;
     virtual bool isLoading() const OVERRIDE;
 
     void clearOwnerRule() { m_ownerRule = 0; }
     Document* ownerDocument() const;
     MediaQuerySet* mediaQueries() const { return m_mediaQueries.get(); }
     void setMediaQueries(PassRefPtr<MediaQuerySet>);
     void setTitle(const String& title) { m_title = title; }
 
     class RuleMutationScope {
         WTF_MAKE_NONCOPYABLE(RuleMutationScope);
     public:
         RuleMutationScope(CSSStyleSheet*);
         RuleMutationScope(CSSRule*);
         ~RuleMutationScope();
 
     private:
         CSSStyleSheet* m_styleSheet;
     };
 
     void willMutateRules();
     void didMutateRules();
-    void didMutate();
+    void didMutate(StyleSheetUpdateType = PartialRuleUpdate);
 
     void clearChildRuleCSSOMWrappers();
     void reattachChildRuleCSSOMWrappers();
 
     StyleSheetContents* contents() const { return m_contents.get(); }
 
     bool isInline() const { return m_isInlineStylesheet; }
     TextPosition startPositionInSource() const { return m_startPosition; }
 
 private:
@@ skipping 37 matching lines @@
 
 inline CSSStyleSheet::RuleMutationScope::~RuleMutationScope()
 {
     if (m_styleSheet)
         m_styleSheet->didMutateRules();
 }
 
 } // namespace
 
 #endif