Implement aria properties setsize and posinset.

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 a5438ac4ada964ee02f7734e009ef76f7e326b59..e03c80043d0a39cfc11c4deea8c6d6324d9fa2b9 100644
--- a/Source/modules/accessibility/AXNodeObject.cpp
+++ b/Source/modules/accessibility/AXNodeObject.cpp
@@ -1265,6 +1265,30 @@ InvalidState AXNodeObject::invalidState() const
     return InvalidStateUndefined;
 }
 
+int AXNodeObject::posInSet() const
+{
+    if (supportsSetSizeAndPosInSet()) {
+        if (hasAttribute(aria_posinsetAttr))
+            return getAttribute(aria_posinsetAttr).toInt();
+        return AXObject::indexInParent();
+    }
+
+    return 0;
+}
+
+int AXNodeObject::setSize() const
+{
+    if (supportsSetSizeAndPosInSet()) {
+        if (hasAttribute(aria_setsizeAttr))
+            return getAttribute(aria_setsizeAttr).toInt();
+
+        const auto& siblings = parentObject()->children();
+        return siblings.size();
+    }
+
+    return 0;
+}
+
 String AXNodeObject::ariaInvalidValue() const
 {
     if (invalidState() == InvalidStateOther)