Use package:sky imports consistently

sky/sdk/lib/widgets/widget.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:sky/base/debug.dart';
+import 'package:sky/base/hit_test.dart';
 import 'package:sky/mojo/activity.dart' as activity;
+import 'package:sky/rendering/box.dart';
+import 'package:sky/rendering/object.dart';
+import 'package:sky/rendering/sky_binding.dart';
 
-import '../base/debug.dart';
-import '../base/hit_test.dart';
-import '../rendering/box.dart';
-import '../rendering/object.dart';
-import '../rendering/sky_binding.dart';
-
-export '../rendering/box.dart' show BoxConstraints, BoxDecoration, Border, BorderSide, EdgeDims;
-export '../rendering/flex.dart' show FlexDirection;
-export '../rendering/object.dart' show Point, Offset, Size, Rect, Color, Paint, Path;
+export 'package:sky/rendering/box.dart' show BoxConstraints, BoxDecoration, Border, BorderSide, EdgeDims;
+export 'package:sky/rendering/flex.dart' show FlexDirection;
+export 'package:sky/rendering/object.dart' show Point, Offset, Size, Rect, Color, Paint, Path;
 
 final bool _shouldLogRenderDuration = false;
 
 typedef Widget Builder();
 typedef void WidgetTreeWalker(Widget);
 
 /// A base class for elements of the widget tree
 abstract class Widget {
 
   Widget({ String key }) : _key = key {
@@ skipping 1111 matching lines @@
     if (root.parent == null) {
       // we haven't attached it yet
       assert(_container.child == null);
       _container.child = root;
     }
     assert(root.parent == _container);
   }
 
   Widget build() => builder();
 }