Rationalize Dart mojo and sky package structure

examples/dart/wget/main.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.
 
 // Run with, e.g.:
 // mojo_shell "mojo:dart_wget http://www.google.com"
 
 import 'dart:async';
 import 'dart:typed_data';
 
-import 'package:mojo/public/dart/application.dart';
-import 'package:mojo/public/dart/bindings.dart';
-import 'package:mojo/public/dart/core.dart';
+import 'package:mojo/application.dart';
+import 'package:mojo/bindings.dart';
+import 'package:mojo/core.dart';
 import 'package:mojom/mojo/network_service.mojom.dart';
 import 'package:mojom/mojo/url_loader.mojom.dart';
 
 class WGet extends Application {
   NetworkServiceProxy _networkService;
   UrlLoaderProxy _urlLoader;
 
   WGet.fromHandle(MojoHandle handle) : super.fromHandle(handle);
 
   void initialize(List<String> args, String url) {
@@ skipping 45 matching lines @@
     _urlLoader = null;
     _networkService.close();
     _networkService = null;
   }
 }
 
 main(List args) {
   MojoHandle appHandle = new MojoHandle(args[0]);
   new WGet.fromHandle(appHandle);
 }