Only 'form associated' elements have a potential form owner.

Source/core/html/HTMLElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2011 Motorola Mobility. 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 724 matching lines @@
     return Element::rendererIsNeeded(style);
 }
 
 RenderObject* HTMLElement::createRenderer(RenderStyle* style)
 {
     if (hasLocalName(wbrTag))
         return new RenderWordBreak(this);
     return RenderObject::createObject(this, style);
 }
 
+HTMLFormElement* HTMLElement::formOwner() const

[tkent, 2013/12/10 23:19:28]

This function always calls a virtual function isFormAssociatedElement(), and
calls another virtual function virtualForm() if this is
isFormAssociatedElement(). It's inefficient.

Why don't you just make formOwner() virtual, and override it in form-associated
elements?

Unfortunately we already have FormAssociatedElement class and
isFormAssociatedElement() doesn't match to it. It's very confusing.

[sof, 2013/12/11 07:55:03]

Agreed, too much indirection here.

As suggested, I've virtualized formOwner() instead, doing away with the explicit
is-form-associated predicate. Looks better?

(The reason there isn't an exact overlap with FormAssociatedElement and the
form-associated predicate in the spec is <label> and <img>.)

+{
+    if (!isFormAssociatedElement())
+        return 0;
+
+    return virtualForm();
+}
+
 HTMLFormElement* HTMLElement::findFormAncestor() const
 {
     for (ContainerNode* ancestor = parentNode(); ancestor; ancestor = ancestor->parentNode()) {
         if (ancestor->hasTagName(formTag))
             return toHTMLFormElement(ancestor);
     }
     return 0;
 }
 
 HTMLFormElement* HTMLElement::virtualForm() const
@@ skipping 320 matching lines @@
 #ifndef NDEBUG
 
 // For use in the debugger
 void dumpInnerHTML(WebCore::HTMLElement*);
 
 void dumpInnerHTML(WebCore::HTMLElement* element)
 {
     printf("%s\n", element->innerHTML().ascii().data());
 }
 #endif