Back button should kill interactive flex app

sky/sdk/example/rendering/interactive_flex.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 'dart:math' as math;
 
+import 'package:sky/mojo/activity.dart' as activity;
 import 'package:sky/mojo/net/image_cache.dart' as image_cache;
 import 'package:sky/painting/text_style.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/paragraph.dart';
 import 'package:sky/rendering/sky_binding.dart';
 
 import 'solid_color_box.dart';
 
@@ skipping 20 matching lines @@
 
 RenderImageGrow image;
 
 Map<int, Touch> touches = new Map();
 void handleEvent(event) {
   if (event is PointerEvent) {
     if (event.type == 'pointermove')
       image.growth = math.max(0.0, image.growth + event.x - touches[event.pointer].x);
     touches[event.pointer] = new Touch(event.x, event.y);
   }
+  if (event.type == "back") {
+    activity.finishCurrentActivity();
+  }
 }
 
 void main() {
   void addFlexChildSolidColor(RenderFlex parent, Color backgroundColor, { int flex: 0 }) {
     RenderSolidColorBox child = new RenderSolidColorBox(backgroundColor);
     parent.add(child);
     child.parentData.flex = flex;
   }
 
   var row = new RenderFlex(direction: FlexDirection.horizontal);
@@ skipping 36 matching lines @@
   column.parentData.flex = 8;
 
   RenderDecoratedBox root = new RenderDecoratedBox(
     decoration: new BoxDecoration(backgroundColor: const Color(0xFFFFFFFF)),
     child: row
   );
 
   new SkyBinding(root: root);
   view.setEventCallback(handleEvent);
 }