Implement aria properties setsize and posinset.

public/web/WebAXObject.h

Index: public/web/WebAXObject.h
diff --git a/public/web/WebAXObject.h b/public/web/WebAXObject.h
index c68c0e4a571f5664031803b32bb2166c6b2fa1b3..336ed93a617bce65b18e7cbe558a1e2dffc0201d 100644
--- a/public/web/WebAXObject.h
+++ b/public/web/WebAXObject.h
@@ -192,6 +192,10 @@ public:
     // exposed by one of the two functions above.
     BLINK_EXPORT WebString placeholder(WebAXNameFrom, WebAXDescriptionFrom);
 
+    // 1-based position in set & Size of set.
+    BLINK_EXPORT int posInSet() const;
+    BLINK_EXPORT int setSize() const;
+
     // Live regions.
     BLINK_EXPORT bool isInLiveRegion() const;
     BLINK_EXPORT bool liveRegionAtomic() const;