Add constants for material colors and shadows

sky/framework/theme/shadows.dart

Index: sky/framework/theme/shadows.dart
diff --git a/sky/framework/theme/shadows.dart b/sky/framework/theme/shadows.dart
new file mode 100644
index 0000000000000000000000000000000000000000..6c0d8ee5f7b1d2d85f686d14daee73ab9d83d98d
--- /dev/null
+++ b/sky/framework/theme/shadows.dart
@@ -0,0 +1,11 @@
+// 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.
+
+const Map<int, String> Shadow = const {
+  1: '0  1px  3px rgba(0,0,0,0.12), 0  1px  2px rgba(0,0,0,0.24)',
+  2: '0  3px  6px rgba(0,0,0,0.16), 0  3px  6px rgba(0,0,0,0.23)',
+  3: '0 10px 20px rgba(0,0,0,0.19), 0  6px  6px rgba(0,0,0,0.23)',
+  4: '0 14px 28px rgba(0,0,0,0.25), 0 10px 10px rgba(0,0,0,0.22)',
+  5: '0 19px 38px rgba(0,0,0,0.30), 0 15px 12px rgba(0,0,0,0.22)',
+};