Implement hashCode on objects stored in a set or used as map keys.

dart/sdk/lib/_internal/compiler/implementation/native_handler.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.
 
 library native;
 
 import 'dart:collection' show Queue;
 import 'dart2jslib.dart' hide SourceString;
 import 'dart_types.dart';
 import 'elements/elements.dart';
@@ skipping 10 matching lines @@
 /// This class is a temporary work-around until we get a more powerful DartType.
 class SpecialType {
   final String name;
   const SpecialType._(this.name);
 
   /// The type Object, but no subtypes:
   static const JsObject = const SpecialType._('=Object');
 
   /// The specific implementation of List that is JavaScript Array:
   static const JsArray = const SpecialType._('=List');
+
+  int get hashCode => name.hashCode;
 }
 
 
 /**
  * This could be an abstract class but we use it as a stub for the dart_backend.
  */
 class NativeEnqueuer {
   /// Initial entry point to native enqueuer.
   void processNativeClasses(Iterable<LibraryElement> libraries) {}
 
@@ skipping 977 matching lines @@
           'native "..." syntax is restricted to functions with zero parameters',
           node: nativeBody);
     }
     LiteralString jsCode = nativeBody.asLiteralString();
     builder.push(new HForeign.statement(
         new js.LiteralStatement(jsCode.dartString.slowToString()),
         <HInstruction>[],
         new SideEffects()));
   }
 }