Teach sky_shell.exe to run from a snapshot

sky/sdk/lib/mojo/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 'dart:async';
 import 'dart:typed_data';
 
 import 'package:mojo/core.dart' as core;
 import 'package:mojom/mojo/network_service.mojom.dart';
 import 'package:mojom/mojo/url_loader.mojom.dart';
 import 'package:mojom/mojo/url_request.mojom.dart';
 import 'package:mojom/mojo/url_response.mojom.dart';
 
 import '../shell.dart' as shell;
 
 class Response {
   ByteData body;
 
   Response(this.body);
 
   String bodyAsString() {
+    if (body == null)
+      return null;
     return new String.fromCharCodes(new Uint8List.view(body.buffer));
   }
 }
 
 Future<UrlResponse> fetch(UrlRequest request) async {
-  NetworkServiceProxy net = new NetworkServiceProxy.unbound();
-  shell.requestService("mojo:authenticated_network_service", net);
+  try {
+    NetworkServiceProxy net = new NetworkServiceProxy.unbound();
+    shell.requestService("mojo:authenticated_network_service", net);
 
-  UrlLoaderProxy loader = new UrlLoaderProxy.unbound();
-  net.ptr.createUrlLoader(loader);
+    UrlLoaderProxy loader = new UrlLoaderProxy.unbound();
+    net.ptr.createUrlLoader(loader);
 
-  UrlResponse response = (await loader.ptr.start(request)).response;
+    UrlResponse response = (await loader.ptr.start(request)).response;
 
-  loader.close();
-  net.close();
-  return response;
+    loader.close();
+    net.close();
+    return response;
+  } catch (e) {
+    return new UrlResponse()..statusCode = 500;
+  }
 }
 
 Future<UrlResponse> fetchUrl(String relativeUrl) async {
   String url = Uri.base.resolve(relativeUrl).toString();
   UrlRequest request = new UrlRequest()
     ..url = url
     ..autoFollowRedirects = true;
   return fetch(request);
 }
 
 Future<Response> fetchBody(String relativeUrl) async {
   UrlResponse response = await fetchUrl(relativeUrl);
   if (response.body == null) return new Response(null);
 
   ByteData data = await core.DataPipeDrainer.drainHandle(response.body);
   return new Response(data);
 }