Add 'part of' in dart2js code.

lib/compiler/implementation/enqueue.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.
 
+part of dart2js;
+
 class EnqueueTask extends CompilerTask {
   final Enqueuer codegen;
   final Enqueuer resolution;
 
   String get name => 'Enqueue';
 
   EnqueueTask(Compiler compiler)
     : codegen = new Enqueuer('codegen enqueuer', compiler,
                              compiler.backend.createItemCompilationContext),
       resolution = new Enqueuer('resolution enqueuer', compiler,
@@ skipping 347 matching lines @@
 
   String toString() => 'Enqueuer($name)';
 
   registerUsedSelector(Selector selector) {
     Element interceptor = compiler.backend.getInterceptor(selector);
     if (interceptor != null) {
       registerStaticUse(interceptor);
     }
   }
 }