Make sure [this] is available for super sends.

dart/tests/language/closure_with_super_send_test.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Test a closurized super send.
+
+class Super {
+  m() => "super";
+}
+
+class Sub extends Super {
+  m() => "sub";
+
+  test() {
+    var x;
+    [0].forEach((e) => x = super.m());
+    return x;
+  }
+}
+
+main() {
+  Expect.equals("super", new Sub().test());
+  Expect.equals("super", new Super().m());
+  Expect.equals("sub", new Sub().m());
+}