Refactoring to support dark theme better

sky/sdk/lib/widgets/drawer_header.dart

Index: sky/sdk/lib/widgets/drawer_header.dart
diff --git a/sky/sdk/lib/widgets/drawer_header.dart b/sky/sdk/lib/widgets/drawer_header.dart
index 730055b3db1256ad793d04c7c0a8aae34ea70b2f..6f9b0e82694a47ac16e88ebd3d6f5e129dab8708 100644
--- a/sky/sdk/lib/widgets/drawer_header.dart
+++ b/sky/sdk/lib/widgets/drawer_header.dart
@@ -2,12 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import '../theme/colors.dart';
 import '../theme/view_configuration.dart';
 import 'basic.dart';
 import 'default_text_style.dart';
 import 'theme.dart';
 
+// TODO(jackson): This class should usually render the user's
+// preferred banner image rather than a solid background
+
 class DrawerHeader extends Component {
 
   DrawerHeader({ String key, this.children }) : super(key: key);
@@ -18,7 +20,7 @@ class DrawerHeader extends Component {
     return new Container(
       height: kStatusBarHeight + kMaterialDrawerHeight,
       decoration: new BoxDecoration(
-        backgroundColor: BlueGrey[50],
+        backgroundColor: Theme.of(this).cardColor,
         border: const Border(
           bottom: const BorderSide(
             color: const Color(0xFFD1D9E1),