Make the TaskDescription background color match the ToolBar on Android

sky/sdk/lib/mojo/activity.dart

Index: sky/sdk/lib/mojo/activity.dart
diff --git a/sky/sdk/lib/mojo/activity.dart b/sky/sdk/lib/mojo/activity.dart
index 7abd84d06f95bd7bdcc1537dd14ce49b35411a36..9136494e61a71c23828a2a7b71880c7b412157d6 100644
--- a/sky/sdk/lib/mojo/activity.dart
+++ b/sky/sdk/lib/mojo/activity.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:sky';
 import 'package:mojom/intents/intents.mojom.dart';
 import 'package:sky/mojo/shell.dart' as shell;
 
@@ -17,6 +18,10 @@ ActivityManagerProxy _initActivityManager() {
 
 final ActivityManagerProxy _activityManager = _initActivityManager();
 
+Color _cachedPrimaryColor;
+String _cachedLabel;
+
+
 void finishCurrentActivity() {
   _activityManager.ptr.finishCurrentActivity();
 }
@@ -24,3 +29,17 @@ void finishCurrentActivity() {
 void startActivity(Intent intent) {
   _activityManager.ptr.startActivity(intent);
 }
+
+void updateTaskDescription(String label, Color color) {
+  if (_cachedPrimaryColor == color && _cachedLabel == label)
+    return;
+
+  _cachedPrimaryColor = color;
+  _cachedLabel = label;
+
+  TaskDescription description = new TaskDescription()
+    ..label = label
+    ..primaryColor = (color != null ? color.value : null);
+
+  _activityManager.ptr.setTaskDescription(description);
+}