Use package:sky imports consistently

sky/sdk/lib/mojo/activity.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';
+
 import 'package:mojom/activity/activity.mojom.dart';
 import 'package:sky/mojo/shell.dart' as shell;
 
 export 'package:mojom/activity/activity.mojom.dart' show Intent, ComponentName, StringExtra;
 
 const int NEW_DOCUMENT = 0x00080000;
 const int NEW_TASK = 0x10000000;
 const int MULTIPLE_TASK = 0x08000000;
 
 ActivityProxy _initActivity() {
@@ skipping 22 matching lines @@
 
   _cachedPrimaryColor = color;
   _cachedLabel = label;
 
   TaskDescription description = new TaskDescription()
     ..label = label
     ..primaryColor = (color != null ? color.value : null);
 
   _activity.ptr.setTaskDescription(description);
 }