Use package:sky imports consistently

sky/sdk/lib/rendering/box.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:math' as math;
 import 'dart:sky' as sky;
 
+import 'package:sky/base/debug.dart';
+import 'package:sky/painting/box_painter.dart';
+import 'package:sky/rendering/object.dart';
 import 'package:vector_math/vector_math.dart';
 
-import '../base/debug.dart';
-import '../painting/box_painter.dart';
-import 'object.dart';
-
-export '../painting/box_painter.dart';
+export 'package:sky/painting/box_painter.dart';
 
 // GENERIC BOX RENDERING
 // Anything that has a concept of x, y, width, height is going to derive from this
 
 // This class should only be used in debug builds
 class _DebugSize extends Size {
   _DebugSize(Size source, this._owner, this._canBeUsedByParent): super.copy(source);
   final RenderBox _owner;
   final bool _canBeUsedByParent;
 }
@@ skipping 1544 matching lines @@
 
   void defaultPaint(PaintingCanvas canvas, Offset offset) {
     RenderBox child = firstChild;
     while (child != null) {
       assert(child.parentData is ParentDataType);
       canvas.paintChild(child, child.parentData.position + offset);
       child = child.parentData.nextSibling;
     }
   }
 }