Migrate language block 46 - canonical_const ... char_escape.

tests/language_2/cascade_in_expression_function_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.
 // Dart test program for testing throw statement
 
 import "package:expect/expect.dart";
 
 makeMap() => new Map()
   ..[3] = 4
   ..[0] = 11;
 
 class MyClass {
   foo() => this
     ..bar(3)
     ..baz(4);
   bar(x) => x;
   baz(y) => y * 2;
 }
 
 main() {
   var o = new MyClass();
   Expect.equals(o.foo(), o);
   var g = makeMap();
   Expect.equals(g[3], 4);
   Expect.equals(g[0], 11);
 }