Use package:sky imports consistently

sky/sdk/lib/mojo/shell.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:sky.internals" as internals;
 
 import "package:mojo/application.dart";
 import "package:mojom/mojo/service_provider.mojom.dart";
 import 'package:mojo/core.dart' as core;
-
-import "embedder.dart";
+import "package:sky/mojo/embedder.dart";
 
 ApplicationConnection _initConnection() {
   int rawHandle = internals.takeServicesProvidedByEmbedder();
   core.MojoHandle proxyHandle = new core.MojoHandle(rawHandle);
   ServiceProviderProxy serviceProvider = null;
   if (proxyHandle.isValid) serviceProvider =
       new ServiceProviderProxy.fromHandle(proxyHandle);
   return new ApplicationConnection(null, serviceProvider);
 }
 
 final ApplicationConnection _connection = _initConnection();
 
 void requestService(String url, Object proxy) {
   if (embedder.shell == null) _connection.requestService(proxy);
   else embedder.connectToService(url, proxy);
 }