bug 1215657 - make AccessibleWrap::accHitTest() work with proxies r=davidb

accessible/windows/msaa/AccessibleWrap.cpp

@@ -1086,11 +1086,15 @@ AccessibleWrap::accHitTest(
   if (IsDefunct())
     return CO_E_OBJNOTCONNECTED;
 
-  // TODO make this work with proxies.
-  if (IsProxy())
-    return E_NOTIMPL;
-
-  Accessible* accessible = ChildAtPoint(xLeft, yTop, eDirectChild);
+  Accessible* accessible = nullptr;
+  if (IsProxy()) {
+    ProxyAccessible* proxy = Proxy()->ChildAtPoint(xLeft, yTop, eDirectChild);
+    if (proxy) {
+      accessible = WrapperFor(proxy);
+    }
+  } else {
+    accessible = ChildAtPoint(xLeft, yTop, eDirectChild);
+  }
 
   // if we got a child
   if (accessible) {