Implement 'tabstop' as an HTML attribute

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index 4d808acc297db2ab0233a5fa054b682d19cfd5d2..a9ed264b00800bd930e3d5054bd2b6ca02e673d1 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -211,13 +211,20 @@ void Element::clearElementFlag(ElementFlags 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 (!hasAttribute(tabstopAttr))

[tkent, 2015/03/31 06:16:32]

hasAttribute -> fastHasAttribute

[kochi, 2015/03/31 08:04:24]

Done.

+            setTabStopInternal(true);
+    }
 }
 
 void Element::setTabIndexExplicitly(short tabIndex)
 {
     ensureElementRareData().setTabIndexExplicitly(tabIndex);
+    if (!hasAttribute(tabstopAttr))

[tkent, 2015/03/31 06:16:32]

Ditto.

[kochi, 2015/03/31 08:04:24]

Done.

+        setTabStopInternal(tabIndex >= 0);
 }
 
 void Element::setTabIndex(int value)
@@ -2092,6 +2099,21 @@ void Element::parseAttribute(const QualifiedName& name, const AtomicString& valu
             // 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);
+            }

[tkent, 2015/03/31 06:16:32]

What should happen if a string other than "true" "" "false" is specified?


I'm asking "invalid value default" in
https://html.spec.whatwg.org/multipage/infrastructure.html#keywords-and-enume...
.

[kochi, 2015/03/31 08:04:24]

If tabstop is not either of "true", "", "false", it falls back to default state,
as if no tabstop is specified.  In the default state, tabStop value depends on
its tabIndex value (e.g. true on tabindex=0, false on tabindex=-1).

Therefore the case (none of "true" "" "false") the attribute is ignored.

Code to handle the case was missing, so added with layout test change.

+        }
     }
 }
 
@@ -2334,12 +2356,21 @@ bool Element::isMouseFocusable() const
 
 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();
 }