Use package:sky imports consistently

sky/sdk/lib/mojo/net/image_cache.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:collection';
 import 'dart:sky' as sky;
 
 import 'package:mojom/mojo/url_response.mojom.dart';
-
-import 'fetch.dart';
+import 'package:sky/mojo/net/fetch.dart';
 
 final HashMap<String, Future<sky.Image>> _cache =
     new HashMap<String, Future<sky.Image>>();
 
 Future<sky.Image> load(String url) {
   return _cache.putIfAbsent(url, () {
     Completer<sky.Image> completer = new Completer<sky.Image>();
     fetchUrl(url).then((UrlResponse response) {
       if (response.statusCode >= 400) {
         print("Failed to load image ${url}");
         completer.complete(null);
       } else {
         new sky.ImageDecoder(response.body.handle.h, completer.complete);
       }
     });
     return completer.future;
   });
 }