Migrate test block 47 and downstream dependencies to Dart 2.0.

tests/language_strong/class_codegen_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.
-
-import "package:expect/expect.dart";
-
-class A {
-  A() : x = 3;
-  foo() => x;
-  var x;
-}
-
-class B extends A {
-  bar() => 499;
-}
-
-class C extends A {
-  bar() => 42;
-}
-
-main() {
-  // We don't instantiate A, but the codegen still needs to emit (parts of) it
-  // for inheritance purposes.
-  var b = new B();
-  var c = new C();
-  Expect.equals(3, b.foo());
-  Expect.equals(3, c.foo());
-  Expect.equals(499, b.bar());
-  Expect.equals(42, c.bar());
-}