Blur immediately if an attribute change made an element unfocasable.

third_party/WebKit/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) 2003-2011, 2013, 2014 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 338 matching lines @@
   virtual bool isPresentationAttribute(const QualifiedName&) const {
     return false;
   }
   virtual void collectStyleForPresentationAttribute(const QualifiedName&,
                                                     const AtomicString&,
                                                     MutableStylePropertySet*) {}
 
   // For exposing to DOM only.
   NamedNodeMap* attributesForBindings() const;
 
-  enum AttributeModificationReason { ModifiedDirectly, ModifiedByCloning };
+  enum class AttributeModificationReason { kDirectly, kByParser, kByCloning };
 
-  // This method is called whenever an attribute is added, changed or removed.
+  // |attributeChanged| is called whenever an attribute is added, changed or
+  // removed. It handles very common attributes such as id, class, name, style,
+  // and slot.
+  //
+  // While the owner document is parsed, this function is called after all
+  // attributes in a start tag were added to the element.
   virtual void attributeChanged(const QualifiedName&,
                                 const AtomicString& oldValue,
                                 const AtomicString& newValue,
-                                AttributeModificationReason = ModifiedDirectly);
+                                AttributeModificationReason);
+
+  // |parseAttribute| is called by |attributeChanged|. If an element
+  // implementation needs to check an attribute update, we should override this

[kochi, 2016/12/21 05:58:09]

nit: avoid "we" and just "override this function" sounds fine. 

[tkent, 2016/12/21 06:51:15]

Will do.

+  // function.
+  //
+  // While the owner document is parsed, this function is called after all
+  // attributes in a start tag were added to the element.
   virtual void parseAttribute(const QualifiedName&,
                               const AtomicString& oldValue,
                               const AtomicString& newValue);
 
   virtual bool hasLegalLinkAttribute(const QualifiedName&) const;
   virtual const QualifiedName& subResourceAttributeName() const;
 
   // Only called by the parser immediately after element construction.
   void parserSetAttributes(const Vector<Attribute>&);
 
@@ skipping 798 matching lines @@
 #define DECLARE_ELEMENT_FACTORY_WITH_TAGNAME(T) \
   static T* create(const QualifiedName&, Document&)
 #define DEFINE_ELEMENT_FACTORY_WITH_TAGNAME(T)                     \
   T* T::create(const QualifiedName& tagName, Document& document) { \
     return new T(tagName, document);                               \
   }
 
 }  // namespace blink
 
 #endif  // Element_h