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

Source/core/accessibility/AXNodeObject.cpp

Index: Source/core/accessibility/AXNodeObject.cpp
diff --git a/Source/core/accessibility/AXNodeObject.cpp b/Source/core/accessibility/AXNodeObject.cpp
index 7ec67e625556cc4d46edcee1077685037cd2a13a..2660f4364a06a71c3c5891100aac4e8f5b72b18e 100644
--- a/Source/core/accessibility/AXNodeObject.cpp
+++ b/Source/core/accessibility/AXNodeObject.cpp
@@ -707,6 +707,14 @@ bool AXNodeObject::isEnabled() const
     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();