Improve performance to remove OPTIONs from a single-selection SELECT.

third_party/WebKit/Source/core/layout/LayoutMenuList.h

 /*
  * This file is part of the select element layoutObject in WebCore.
  *
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 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 21 matching lines @@
 
 class HTMLSelectElement;
 class LayoutText;
 
 class CORE_EXPORT LayoutMenuList final : public LayoutFlexibleBox {
 public:
     explicit LayoutMenuList(Element*);
     ~LayoutMenuList() override;
 
     HTMLSelectElement* selectElement() const;
-    void setOptionsChanged(bool changed) { m_optionsChanged = changed; }
+    void setOptionsChanged(bool);
     void didSetSelectedIndex(int optionIndex);
     String text() const;
 
     const char* name() const override { return "LayoutMenuList"; }
 
     LayoutUnit clientPaddingLeft() const;
     LayoutUnit clientPaddingRight() const;
 
 private:
     bool isOfType(LayoutObjectType type) const override { return type == LayoutObjectMenuList || LayoutFlexibleBox::isOfType(type); }
@@ skipping 21 matching lines @@
     {
         return LayoutBlock::baselinePosition(baseline, firstLine, direction, position);
     }
     int firstLineBoxBaseline() const override { return LayoutBlock::firstLineBoxBaseline(); }
     int inlineBlockBaseline(LineDirectionMode direction) const override { return LayoutBlock::inlineBlockBaseline(direction); }
 
     void createInnerBlock();
     void adjustInnerStyle();
     void setText(const String&);
     void setTextFromOption(int optionIndex);
-    void updateOptionsHeightWidth();
+    void updateOptionsHeightWidth() const;
     float computeTextHeight(const TextRun&, const ComputedStyle&) const;
     float computeTextWidth(const TextRun&, const ComputedStyle&) const;
-    void updateText();
     void setIndexToSelectOnCancel(int listIndex);
 
     void didUpdateActiveOption(int optionIndex);
 
     LayoutText* m_buttonText;
     LayoutBlock* m_innerBlock;
 
-    bool m_optionsChanged : 1;
+    mutable bool m_optionsChanged : 1;
     bool m_isEmpty : 1;
     bool m_hasUpdatedActiveOption : 1;
-    int m_optionsHeight;
-    int m_optionsWidth;
+    // m_optionsHeight and m_optionsWidth are calculated and cached on demand.
+    // updateOptionsHeightWidth() should be called before reading them.
+    mutable int m_optionsHeight;
+    mutable int m_optionsWidth;
 
     int m_lastActiveIndex;
 
     RefPtr<ComputedStyle> m_optionStyle;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutMenuList, isMenuList());
 
 } // namespace blink
 
 #endif