improve divider appearance in dark mode

sky/sdk/lib/theme/theme_data.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 'typography.dart' as typography;
 import 'colors.dart' as colors;
 
 enum ThemeBrightness { dark, light }
 
 class ThemeData {
 
   ThemeData({
     ThemeBrightness brightness,
     Map<int, Color> primarySwatch,
     Color accentColor,
     Color floatingActionButtonColor,
     typography.TextTheme text,
     typography.TextTheme toolbarText })
     : this.brightness = brightness,
       this.primarySwatch = primarySwatch,
       canvasColor = brightness == ThemeBrightness.dark ? colors.Grey[850] : colors.Grey[50],
       cardColor = brightness == ThemeBrightness.dark ? colors.Grey[800] : colors.White,
+      dividerColor = brightness == ThemeBrightness.dark ? const Color(0x1FFFFFFF) : const Color(0x1F000000),
       text = brightness == ThemeBrightness.dark ? typography.white : typography.black {
     assert(brightness != null);
 
     if (primarySwatch == null) {
       _primaryColor = brightness == ThemeBrightness.dark ? colors.Grey[900] : colors.Grey[100];
     } else {
       _primaryColor = primarySwatch[500];
     }
 
     if (accentColor == null) {
@@ skipping 19 matching lines @@
   }
 
   factory ThemeData.light() => new ThemeData(primarySwatch: colors.Blue, brightness: ThemeBrightness.light);
   factory ThemeData.dark() => new ThemeData(brightness: ThemeBrightness.dark);
   factory ThemeData.fallback() => new ThemeData.light();
 
   final ThemeBrightness brightness;
   final Map<int, Color> primarySwatch;
   final Color canvasColor;
   final Color cardColor;
+  final Color dividerColor;
   final typography.TextTheme text;
 
   Color _primaryColor;
   Color get primaryColor => _primaryColor;
 
   Color _accentColor;
   Color get accentColor => _accentColor;
 
   Color _floatingActionButtonColor;
   Color get floatingActionButtonColor => _floatingActionButtonColor;
 
   typography.TextTheme _toolbarText;
   typography.TextTheme get toolbarText => _toolbarText;
 }