Stop using the Hashable interface.

tests/compiler/dart2js_foreign/native_parameter_names_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.
 
 // Test that parameters in native methods are not mangled. This test is needed
 // until we change all libraries to using the JS foreign element.
 
 @native("*A")
-class A  {
+class A {
   @native("return name;")
   foo(name);
   @native("return undefined;")
   bar(undefined);
 }
 
 @native A makeA();
 
 @native("""
 function A() {}
 makeA = function(){return new A;};
 """)
 void setup();
 
 
 main() {
   setup();
   A a = makeA();
   Expect.equals(42, a.foo(42));
   Expect.equals(42, a.bar(42));
 }