Rationalize Dart mojo and sky package structure

sky/framework/net/fetch.dart

-// Copyright 2015 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.
-
-import '../shell.dart' as shell;
-import 'dart:async';
-import 'dart:sky' as sky;
-import 'dart:typed_data';
-import 'package:mojo/public/dart/core.dart' as core;
-import 'package:mojom/mojo/network_service.mojom.dart';
-import 'package:mojom/mojo/url_loader.mojom.dart';
-
-class Response {
-  ByteData body;
-
-  Response(this.body);
-
-  String bodyAsString() {
-    return new String.fromCharCodes(new Uint8List.view(body.buffer));
-  }
-}
-
-Future<Response> fetch(String relativeUrl) async {
-  String url = new sky.URL(relativeUrl, sky.document.baseURI).href;
-
-  var net = new NetworkServiceProxy.unbound();
-  shell.requestService("mojo:network_service", net);
-
-  var loader = new UrlLoaderProxy.unbound();
-  net.ptr.createUrlLoader(loader);
-
-  var request = new UrlRequest()
-    ..url = url
-    ..autoFollowRedirects = true;
-  var response = (await loader.ptr.start(request)).response;
-
-  loader.close();
-  net.close();
-
-  if (response.body == null) return new Response(null);
-
-  ByteData data = await core.DataPipeDrainer.drainHandle(response.body);
-  return new Response(data);
-}