Migrate language block 45 - call_argument ... call_with.

tests/language_strong/call_function2_test.dart

-// Copyright (c) 2016, 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.
-
-import "package:expect/expect.dart";
-
-typedef Object Func(Object x);
-
-class Bar {
-  int x = 42;
-
-  Object call(Object x) {
-    return 'Bar $x';
-  }
-}
-
-Object baz(Object x) => x;
-
-var map = <String, Func>{'baz': baz, 'bar': new Bar()};
-
-Object test(String str, Object arg) {
-  return map[str].call(arg);
-}
-
-void main() {
-  Expect.equals(42, test('baz', 42));
-  Expect.equals('Bar 42', test('bar', 42));
-}