Blur immediately if an attribute change made an element unfocasable.

third_party/WebKit/Source/core/html/HTMLElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004-2008, 2013, 2014 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
@@ skipping 408 matching lines @@
         {onwheelAttr, EventTypeNames::wheel},
     };
 
     for (const auto& name : attrToEventNames)
       attributeNameToEventNameMap.set(name.attr.localName(), name.event);
   }
 
   return attributeNameToEventNameMap.get(attrName.localName());
 }
 
+void HTMLElement::attributeChanged(const QualifiedName& name,
+                                   const AtomicString& oldValue,
+                                   const AtomicString& newValue,
+                                   AttributeModificationReason reason) {
+  Element::attributeChanged(name, oldValue, newValue, reason);
+  if (reason != AttributeModificationReason::kDirectly)
+    return;
+  if (adjustedFocusedElementInTreeScope() != this)
+    return;
+  if (name == hiddenAttr && !newValue.isNull()) {
+    blur();
+  } else if (name == contenteditableAttr) {
+    // The attribute change may cause supportsFocus() to return false
+    // for the element which had focus.
+    //
+    // TODO(tkent): We should avoid updating style.  We'd like to check only
+    // DOM-level focusability here.
+    document().updateStyleAndLayoutTreeForNode(this);
+    if (!supportsFocus())
+      blur();
+  }
+}
+
 void HTMLElement::parseAttribute(const QualifiedName& name,
                                  const AtomicString& oldValue,
                                  const AtomicString& value) {
   if (name == tabindexAttr || name == XMLNames::langAttr)
     return Element::parseAttribute(name, oldValue, value);
 
   if (name == dirAttr) {
     dirAttributeChanged(value);
   } else if (name == langAttr) {
     pseudoStateChanged(CSSSelector::PseudoLang);
@@ skipping 753 matching lines @@
 
 #ifndef NDEBUG
 
 // For use in the debugger
 void dumpInnerHTML(blink::HTMLElement*);
 
 void dumpInnerHTML(blink::HTMLElement* element) {
   printf("%s\n", element->innerHTML().ascii().data());
 }
 #endif