Make the TaskDescription background color match the ToolBar on Android

sky/sdk/lib/widgets/task_description.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 'package:mojom/intents/intents.mojom.dart' as intents;
+import 'package:sky/mojo/shell.dart' as shell;
+import 'package:sky/widgets/widget.dart';
+import 'package:sky/widgets/theme.dart';
+
+class TaskDescription extends StatefulComponent {
+  Widget child;
+  String label;
+  Color _cachedPrimaryColor;
+  String _cachedLabel;
+
+  TaskDescription({this.label, this.child});
+
+  void syncFields(TaskDescription source) {
+    child = source.child;
+    label = source.label;
+  }
+
+  void updateTaskDescription(String label, Color color) {

[abarth-chromium, 2015/07/07 19:57:45]

Can we put this code in sky/sdk/lib/mojo/activity.dart ?  We can store
_cachedPrimaryColor and _cachedLabel as statics in that library.

+    if (_cachedPrimaryColor == color && _cachedLabel == label)
+      return;
+
+    _cachedPrimaryColor = color;
+    _cachedLabel = label;
+
+    intents.ActivityManagerProxy activityManager =
+      new intents.ActivityManagerProxy.unbound();
+    intents.TaskDescription description = new intents.TaskDescription()
+      ..label = label
+      ..primaryColor = (color != null ? color.value : null);
+
+    shell.requestService(null, activityManager);
+    activityManager.ptr.setTaskDescription(description);
+  }
+
+  Widget build() {
+    updateTaskDescription(label, Theme.of(this).primaryColor);
+    return child;
+  }
+}