Support aria-grabbed attribute.

Source/modules/accessibility/AXNodeObject.cpp

Index: Source/modules/accessibility/AXNodeObject.cpp
diff --git a/Source/modules/accessibility/AXNodeObject.cpp b/Source/modules/accessibility/AXNodeObject.cpp
index 6e79ce19f6a1582343e14a50267155993d77f1e6..269e81a68ac453d64ecf20362e459ff6bc229a88 100644
--- a/Source/modules/accessibility/AXNodeObject.cpp
+++ b/Source/modules/accessibility/AXNodeObject.cpp
@@ -1137,6 +1137,17 @@ AccessibilityRole AXNodeObject::ariaRoleAttribute() const
     return m_ariaRole;
 }
 
+AccessibilityOptionalBool AXNodeObject::isAriaGrabbed() const
+{
+    const AtomicString& grabbed = getAttribute(aria_grabbedAttr);
+    if (equalIgnoringCase(grabbed, "true"))
+        return OptionalBoolTrue;
+    if (equalIgnoringCase(grabbed, "false"))
+        return OptionalBoolFalse;
+
+    return OptionalBoolUndefined;
+}
+
 // When building the textUnderElement for an object, determine whether or not
 // we should include the inner text of this given descendant object or skip it.
 static bool shouldUseAccessibilityObjectInnerText(AXObject* obj)