Stop using the Hashable interface.

tests/compiler/dart2js_foreign/native_use_native_name_in_table_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.
 
 // Test that we put native names and not Dart names into the dynamic
 // dispatch table.
 
 @native("*NativeA")
-class A  {
+class A {
   @native foo();
 }
 
 @native("*NativeB")
 class B extends A  {
 }
 
 @native A makeA() { return new A(); }
 @native B makeB() { return new B(); }
 
@@ skipping 25 matching lines @@
   var a = makeA();
   Expect.equals(42, a.foo());
   A aa = a;
   Expect.equals(42, aa.foo());  
 
   var b = makeB();
   Expect.equals(42, b.foo());
   B bb = b;
   Expect.equals(42, bb.foo());  
 }