Add isExpanded() API to WebAXObject.h to get aria-expanded attribute.

Source/core/accessibility/AXNodeObject.cpp

 /*
 * Copyright (C) 2012, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 689 matching lines @@
     if (equalIgnoringCase(getAttribute(aria_disabledAttr), "true"))
         return false;
 
     Node* node = this->node();
     if (!node || !node->isElementNode())
         return true;
 
     return !toElement(node)->isDisabledFormControl();
 }
 
+bool AXNodeObject::isExpanded() const
+{
+    if (equalIgnoringCase(getAttribute(aria_expandedAttr), "true"))
+        return true;
+
+    return false;
+}
+
 bool AXNodeObject::isIndeterminate() const
 {
     Node* node = this->node();
     if (!isHTMLInputElement(node))
         return false;
 
     return toHTMLInputElement(node)->shouldAppearIndeterminate();
 }
 
 bool AXNodeObject::isPressed() const
@@ skipping 1030 matching lines @@
     float range = maxValueForRange() - minValueForRange();
     float value = valueForRange();
 
     value += range * (percentChange / 100);
     setValue(String::number(value));
 
     axObjectCache()->postNotification(node(), AXObjectCache::AXValueChanged, true);
 }
 
 } // namespace blink