Migrate language block 46 - canonical_const ... char_escape.

tests/language/canonical_const3_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.
-//
-// Check proper canonicalization (fields must be canonicalized as well).
-
-import "package:expect/expect.dart";
-
-main() {
-  Expect.isFalse(identical(new Duration(days: 1), new Duration(days: 1)));
-  Expect.isTrue(identical(const Duration(days: 2), const Duration(days: 2)));
-  Expect.isTrue(identical(const B(3.0), const B(3.0)));
-  Expect.isTrue(identical(const F(main), const F(main)));
-}
-
-class A {
-  final a;
-  const A(v) : a = v + 3.4;
-}
-
-class B extends A {
-  final b;
-  const B(v)
-      : super(v),
-        b = v + 1.0;
-}
-
-class F {
-  final f;
-  const F(v) : f = v;
-}