Stop using the Hashable interface.

tests/compiler/dart2js_foreign/native_field_rename_1_test.dart

 // Copyright (c) 2011, 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.
 
 // A native method prevents other members from having that name, including
 // fields.  However, native fields keep their name.  The implication: a getter
 // for the field must be based on the field's name, not the field's jsname.
 
 @native("*A")
-class A  {
+class A {
   int key;                    //  jsname is 'key'
   int getKey() => key;
 }
 
 class B {
   int key;                    //  jsname is not 'key'
   B([this.key = 222]);
   int getKey() => key;
 }
 
 @native("*X")
-class X  {
+class X {
   @native('key') int native_key_method();
   // This should cause B.key to be renamed, but not A.key.
 
   @natve('key') int key();
 }
 
 @native A makeA();
 @native X makeX();
 
 
@@ skipping 40 matching lines @@
   Expect.equals(111, a.getKey());
   Expect.equals(222, b.getKey());
 }
 
 main() {
   setup();
 
   testTyped();
   testDynamic();
 }