Migrate language block 45 - call_argument ... call_with.

tests/language_2/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));
 }