Revert "Change some platform libraries to use `part of URI`."

sdk/lib/vmservice/message.dart

 // Copyright (c) 2013, 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 "dart:_vmservice";
+part of dart._vmservice;
 
 class Message {
   final Completer _completer = new Completer.sync();
   bool get completed => _completer.isCompleted;
 
   /// Future of response.
   Future<String> get response => _completer.future;
   Client client;
 
   // Client-side identifier for this message.
@@ skipping 168 matching lines @@
 
   void setErrorResponse(int code, String details) {
     _completer
         .complete(encodeRpcError(this, code, details: '$method: $details'));
   }
 }
 
 external bool sendIsolateServiceMessage(SendPort sp, List m);
 external void sendRootServiceMessage(List m);
 external void sendObjectRootServiceMessage(List m);