Migrate test block 9 to Dart 2.0

tests/corelib_2/hashcode_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";
 
 class Override {
   int hash;
   int get superHash => super.hashCode;
   int get hashCode => hash;
 
   int foo() => hash; //   Just some function that can be closurized.
 
-  bool operator ==(Object other) =>
-      other is Override && (other as Override).hash == hash;
+  bool operator ==(Object other) => other is Override && other.hash == hash;
 }
 
 int bar() => 42; // Some global function.
 
 main() {
   var o = new Object();
   var hash = o.hashCode;
   // Doesn't change.
   Expect.equals(hash, o.hashCode);
   Expect.equals(hash, identityHashCode(o));
@@ skipping 13 matching lines @@
   }
   // These do, or might do, but we can still use hashCodeOf and get the same
   // result each time.
   samples = ["string", "", (x) => 42, c.foo, bar];
   for (var v in samples) {
     print(v);
     Expect.equals(v.hashCode, v.hashCode);
     Expect.equals(identityHashCode(v), identityHashCode(v));
   }
 }