Fix argument test for the captured parameter of an outer function (issue 8007).

tests/language/argument_definition5_test.dart

+// Copyright (c) 2013, 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.
+
+var x = "";
+
+test(String str, [onError(String)]) {
+  return (() {
+    try {
+      throw "";
+    } catch(e) {
+      if (?onError) {
+        onError(str);
+      } else {
+        x = "${str} error";
+      }
+    }
+  });
+}
+
+ignoreError(String str) {
+  x = "${str} error ignored";
+}
+
+main() {
+  Expect.equals("", x);
+  test("test")();
+  Expect.equals("test error", x);
+  test("test", ignoreError)();
+  Expect.equals("test error ignored", x);
+}