Migrate test block 9 to Dart 2.0

tests/corelib_strong/hashcode_boxed_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.
-
-import "package:expect/expect.dart";
-
-double fib(double n) {
-  return n <= 1.0 ? 1.0 : fib(n - 1) + fib(n - 2);
-}
-
-main() {
-  // Compute the same value in a way that won't be optimized away so the results
-  // are different objects in memory.
-  var a = fib(5.0) + 1.0;
-  var b = fib(4.0) + 4.0;
-
-  Expect.isTrue(identical(a, b));
-  Expect.equals(identityHashCode(a), identityHashCode(b));
-  Expect.equals(a, b);
-  Expect.equals(a.hashCode, b.hashCode);
-}