Migrate test block 9 to Dart 2.0

tests/corelib_2/hash_set_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.
 //
 // VMOptions=
 
 // Tests of hash set behavior, with focus in iteration and concurrent
 // modification errors.
 
 library hash_map2_test;
@@ skipping 283 matching lines @@
   set.add(1); // Integers are identical if equal.
   Expect.equals(2, set.length);
   var complex = 4;
   complex = set.length == 2 ? complex ~/ 4 : 87; // Avoid compile-time constant.
   Expect.isTrue(set.contains(complex)); // 1 is in set, even if computed.
   set.clear();
 
   // All compile time constants are identical to themselves.
   var constants = [
     double.INFINITY,
-                   double.NAN, -0.0, //# 01: ok
+    double.NAN, -0.0, //# 01: ok
     0.0, 42, "", null, false, true, #bif, testIdentitySet
   ];
   set.addAll(constants);
   Expect.equals(constants.length, set.length);
   for (var c in constants) {
     Expect.isTrue(set.contains(c), "constant: $c");
   }
   Expect.isTrue(set.containsAll(constants), "constants: $set");
   set.clear();
 
@@ skipping 39 matching lines @@
   // Can't make a bad compareTo that isn't invalid.
   int compareTo(BadHashCode other) => id - other.id;
 }
 
 class Mutable {
   int id;
   Mutable(this.id);
   int get hashCode => id;
   bool operator ==(other) => other is Mutable && id == other.id;
 }