Rationalize Dart mojo and sky package structure

mojo/public/dart/lib/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;
@@ skipping 110 matching lines @@
     return response.serializeWithHeader(header);
   }
 
   String toString() {
     var superString = super.toString();
     return "Stub(${superString})";
   }
 
   int get version;
 }