[generators] Always call function with closure context when resuming.

test/mjsunit/regress/regress-681171-2.js

Index: test/mjsunit/regress/regress-681171-2.js
diff --git a/test/mjsunit/regress/regress-681171-2.js b/test/mjsunit/regress/regress-681171-2.js
new file mode 100644
index 0000000000000000000000000000000000000000..2f69b68f40d81691d539364a11534b8b9f43e059
--- /dev/null
+++ b/test/mjsunit/regress/regress-681171-2.js
@@ -0,0 +1,12 @@
+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --always-opt --function-context-specialization --verify-heap
+
+function* gen() {
+  for (var i = 0; i < 3; ++i) {
+    yield i
+  }
+}
+gen().next();