Use package:sky imports consistently

sky/sdk/lib/theme/shadows.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' show Color, Offset;
 
-import '../painting/box_painter.dart';
+import 'package:sky/painting/box_painter.dart';
 
 const Map<int, List<BoxShadow>> shadows = const {
   1: const [
     const BoxShadow(
       color: const Color(0x1F000000),
       offset: const Offset(0.0, 1.0),
       blur: 3.0),
     const BoxShadow(
       color: const Color(0x3D000000),
       offset: const Offset(0.0, 1.0),
@@ skipping 33 matching lines @@
     const BoxShadow(
       color: const Color(0x4E000000),
       offset: const Offset(0.0, 19.0),
       blur: 28.0),
     const BoxShadow(
       color: const Color(0x38000000),
       offset: const Offset(0.0, 15.0),
       blur: 12.0),
   ],
 };