Add a test case for the scope of a closure generator

hphp/test/vm/closure_gen_scope.php

@@ -0,0 +1,22 @@
+<?php
+
+class X {
+  private $priv = 'X';
+  function foo() {
+    return function ($x) {
+      yield $x->priv;
+    };
+  }
+}
+
+class Y extends X { private $priv = 'Y'; }
+class Z extends X { private $priv = 'Z'; }
+
+function test($x) {
+  $f = $x->foo();
+  foreach ($f($x) as $v) var_dump($v);
+}
+
+test(new X);
+test(new Y);
+test(new Z);

hphp/test/vm/closure_gen_scope.php.exp

@@ -0,0 +1,3 @@
+string(1) "X"
+string(1) "X"
+string(1) "X"