Dart: Better handle leak checks. close() is async.

mojo/public/dart/src/stub.dart

 // Copyright 2014 The Chromium Authors. 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 bindings;
 
 abstract class Stub extends core.MojoEventStreamListener {
   int _outstandingResponseFutures = 0;
   bool _isClosing = false;
+  Completer _closeCompleter;
 
   Stub.fromEndpoint(core.MojoMessagePipeEndpoint endpoint)
       : super.fromEndpoint(endpoint);
 
   Stub.fromHandle(core.MojoHandle handle) : super.fromHandle(handle);
 
   Stub.unbound() : super.unbound();
 
   Future<Message> handleMessage(ServiceMessage message);
 
@@ skipping 24 matching lines @@
           endpoint.write(
               response.buffer, response.buffer.lengthInBytes, response.handles);
           if (!endpoint.status.isOk) {
             throw 'message pipe write failed: ${endpoint.status}';
           }
           if (_isClosing && (_outstandingResponseFutures == 0)) {
             // This was the final response future for which we needed to send
             // a response. It is safe to close.
             super.close();
             _isClosing = false;
+            _closeCompleter.complete(null);
+            _closeCompleter = null;
           }
         }
       });
     } else if (_isClosing && (_outstandingResponseFutures == 0)) {
       // We are closing, there is no response to send for this message, and
       // there are no outstanding response futures. Do the close now.
       super.close();
       _isClosing = false;
+      _closeCompleter.complete(null);
+      _closeCompleter = null;
     }
   }
 
   void handleWrite() {
     throw 'Unexpected write signal in client.';
   }
 
   // NB: |nodefer| should only be true when calling close() while handling an
   // exception thrown from handleRead(), e.g. when we receive a malformed
   // message.
-  void close({bool nodefer: false}) {
+  Future close({bool nodefer: false}) {
     if (isOpen &&
         !nodefer &&
         (isInHandler || (_outstandingResponseFutures > 0))) {
       // Either close() is being called from within handleRead() or
       // handleWrite(), or close() is being called while there are outstanding
       // response futures. Defer the actual close until all response futures
       // have been resolved.
       _isClosing = true;
+      _closeCompleter = new Completer();
+      return _closeCompleter.future;
     } else {
-      super.close();
+      return super.close();
     }
   }
 
   Message buildResponse(Struct response, int name) {
     var header = new MessageHeader(name);
     return response.serializeWithHeader(header);
   }
 
   Message buildResponseWithId(Struct response, int name, int id, int flags) {
     var header = new MessageHeader.withRequestId(name, flags, id);
     return response.serializeWithHeader(header);
   }
 
   String toString() {
     var superString = super.toString();
     return "Stub(${superString})";
   }
 }