Stop using the Hashable interface.

tests/compiler/dart2js_foreign/native_no_such_method_exception3_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.
 
 @native("*A")
-class A  {
+class A {
   bar() => 42;
 }
 
 @native("*B")
-class B  {
+class B {
   foo() => 42;
 }
 
 class C {
   static create() => new C();
   noSuchMethod(x, y) => "$x:$y";
 }
 
 @native makeA();
 
@@ skipping 11 matching lines @@
   try {
     a.foo();
   } on NoSuchMethodError catch (e) {
     exception = e;
   }
   Expect.isNotNull(exception);
   var c = C.create();
   Expect.equals("foo:[1, 2]", c.foo(1, 2));
   Expect.equals("foo:[3, 4, 5]", c.foo(3, 4, 5));
 }