Implement 'tabstop' as an HTML attribute

Source/core/dom/Element.cpp

 /*
  * 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)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 193 matching lines @@
 
 void Element::clearElementFlag(ElementFlags mask)
 {
     if (!hasRareData())
         return;
     elementRareData()->clearElementFlag(mask);
 }
 
 void Element::clearTabIndexExplicitlyIfNeeded()
 {
-    if (hasRareData())
+    if (hasRareData()) {
         elementRareData()->clearTabIndexExplicitly();
+        // As tabindex is removed, unless there is an tabstop attribute,
+        // revert tabstop to default to match tabindex at this point (0).
+        if (!fastHasAttribute(tabstopAttr))
+            setTabStopInternal(true);
+    }
 }
 
 void Element::setTabIndexExplicitly(short tabIndex)
 {
     ensureElementRareData().setTabIndexExplicitly(tabIndex);
+    if (!fastHasAttribute(tabstopAttr))
+        setTabStopInternal(tabIndex >= 0);
 }
 
 void Element::setTabIndex(int value)
 {
     setIntegralAttribute(tabindexAttr, value);
 }
 
 short Element::tabIndex() const
 {
     return hasRareData() ? elementRareData()->tabIndex() : 0;
@@ skipping 1854 matching lines @@
             clearTabIndexExplicitlyIfNeeded();
             if (treeScope().adjustedFocusedElement() == this) {
                 // We might want to call blur(), but it's dangerous to dispatch
                 // events here.
                 document().setNeedsFocusedElementCheck();
             }
         } else if (parseHTMLInteger(value, tabindex)) {
             // Clamp tabindex to the range of 'short' to match Firefox's behavior.
             setTabIndexExplicitly(max(static_cast<int>(std::numeric_limits<short>::min()), std::min(tabindex, static_cast<int>(std::numeric_limits<short>::max()))));
         }
+    } else if (RuntimeEnabledFeatures::tabStopAttributeEnabled() && name == tabstopAttr) {
+        if (!hasAttribute(tabstopAttr)) {
+            // tabstop attribute removed.
+            clearElementFlag(TabStopWasSetExplicitly);
+            setTabStopInternal(tabIndex() >= 0);
+        } else {
+            // Treat empty attribute as true.
+            if (equalIgnoringCase(value, "true") || equalIgnoringCase(value, "")) {
+                setTabStopInternal(true);
+                setElementFlag(TabStopWasSetExplicitly, true);
+            } else if (equalIgnoringCase(value, "false")) {
+                setTabStopInternal(false);
+                setElementFlag(TabStopWasSetExplicitly, true);
+            } else {
+                // When value is other than "true", "false", "", the value is ignored and
+                // falls back the default state.
+                clearElementFlag(TabStopWasSetExplicitly);
+                setTabStopInternal(tabIndex() >= 0);
+            }
+        }
     }
 }
 
 bool Element::parseAttributeName(QualifiedName& out, const AtomicString& namespaceURI, const AtomicString& qualifiedName, ExceptionState& exceptionState)
 {
     AtomicString prefix, localName;
     if (!Document::parseQualifiedName(qualifiedName, prefix, localName, exceptionState))
         return false;
     ASSERT(!exceptionState.hadException());
 
@@ skipping 222 matching lines @@
     return isFocusable() && tabIndex() >= 0;
 }
 
 bool Element::isMouseFocusable() const
 {
     return isFocusable();
 }
 
 bool Element::tabStop() const
 {
-    // Any element which never supports focus will always return false.
-    return supportsFocus() && (hasRareData() ? elementRareData()->tabStop() : true);
+    if (hasElementFlag(TabStopWasSetExplicitly))
+        return elementRareData()->tabStop();
+    return tabIndex() >= 0;
 }
 
 void Element::setTabStop(bool flag)
 {
+    // Reflect the value in the HTML attribute. Note that we cannot use setBooleanAttribute()
+    // because the tabstop attribute is an enumerated attribute.
+    // After tabstop attribute is set, the property value is modified accordingly.
+    setAttribute(tabstopAttr, flag ? "true" : "false");
+}
+
+void Element::setTabStopInternal(bool flag)
+{
     ensureElementRareData().setTabStop(flag);
     focusStateChanged();
 }
 
 void Element::dispatchFocusEvent(Element* oldFocusedElement, WebFocusType type)
 {
     RefPtrWillBeRawPtr<FocusEvent> event = FocusEvent::create(EventTypeNames::focus, false, false, document().domWindow(), 0, oldFocusedElement);
     EventDispatcher::dispatchEvent(*this, FocusEventDispatchMediator::create(event.release()));
 }
 
@@ skipping 1106 matching lines @@
 {
 #if ENABLE(OILPAN)
     if (hasRareData())
         visitor->trace(elementRareData());
     visitor->trace(m_elementData);
 #endif
     ContainerNode::trace(visitor);
 }
 
 } // namespace blink