Consistently cache ElementData::length() before loops

Source/core/dom/Element.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2013 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
@@ skipping 136 matching lines @@
     const AtomicString& getClassAttribute() const;
 
     bool shouldIgnoreAttributeCase() const;
 
     // Call this to get the value of the id attribute for style resolution purposes.
     // The value will already be lowercased if the document is in compatibility mode,
     // so this function is not suitable for non-style uses.
     const AtomicString& idForStyleResolution() const;
 
     // Internal methods that assume the existence of attribute storage, one should use hasAttributes()
-    // before calling them.
+    // before calling them. This is not a trivial getter and its return value should be cached for
+    // performance.
     size_t attributeCount() const;
     const Attribute* attributeItem(unsigned index) const;
     const Attribute* getAttributeItem(const QualifiedName&) const;
     size_t getAttributeItemIndex(const QualifiedName& name) const { return elementData()->getAttributeItemIndex(name); }
     size_t getAttributeItemIndex(const AtomicString& name, bool shouldIgnoreAttributeCase) const { return elementData()->getAttributeItemIndex(name, shouldIgnoreAttributeCase); }
 
     void scrollIntoView(bool alignToTop = true);
     void scrollIntoViewIfNeeded(bool centerIfNeeded = true);
 
     void scrollByLines(int lines);
@@ skipping 687 matching lines @@
 }
 
 inline bool isShadowHost(const Element* element)
 {
     return element && element->shadow();
 }
 
 } // namespace
 
 #endif