Rationalize Dart mojo and sky package structure

mojo/public/dart/lib/src/application.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 application;
 
 class _ApplicationImpl implements application_mojom.Application {
   application_mojom.ApplicationStub _stub;
   shell_mojom.ShellProxy shell;
   Application _application;
@@ skipping 113 matching lines @@
       ServiceProviderProxy exposedServices, String resolvedUrl) {
     var connection = new ApplicationConnection(services, exposedServices);
     _applicationConnections.add(connection);
     acceptConnection(requestorUrl, resolvedUrl, connection);
   }
 
   // Override this method to provide services on |connection|.
   void acceptConnection(String requestorUrl, String resolvedUrl,
       ApplicationConnection connection) {}
 }