Stop using the Hashable interface.

tests/compiler/dart2js_foreign/native_wrapping_function3_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.
 
 typedef void Callback0();
 typedef void Callback1(arg1);
 typedef void Callback2(arg1, arg2);
 
 @native("*A")
-class A  {
+class A {
   @native foo1(Callback1 closure, [arg1 = 0]);
   @native foo2(Callback2 closure, [arg1 = 0, arg2 = 1]);
 }
 
 @native makeA();
 
 @native("""
 function A() {}
 A.prototype.foo1 = function(closure, arg1) { return closure(arg1); };
 A.prototype.foo2 = function(closure, arg1, arg2) {
@@ skipping 23 matching lines @@
   Expect.equals(43, aa.foo1((arg1) => arg1, arg1: 43));
   Expect.equals(0, aa.foo1((arg1) => arg1));
 
   Expect.equals(44, aa.foo2((arg1, arg2) => arg1 + arg2, 21, 23));
   Expect.equals(22, aa.foo2((arg1, arg2) => arg1 + arg2, 21));
   Expect.equals(22, aa.foo2((arg1, arg2) => arg1 + arg2, arg1: 21));
   Expect.equals(21, aa.foo2((arg1, arg2) => arg1 + arg2, arg2: 21));
   Expect.equals(44, aa.foo2((arg1, arg2) => arg1 + arg2, arg1: 21, arg2: 23));
   Expect.equals(44, aa.foo2((arg1, arg2) => arg1 - arg2, arg2: 22, arg1: 66));
 }