Back button should kill interactive flex app

sky/sdk/example/rendering/interactive_flex.dart

Index: sky/sdk/example/rendering/interactive_flex.dart
diff --git a/sky/sdk/example/rendering/interactive_flex.dart b/sky/sdk/example/rendering/interactive_flex.dart
index 6553c8bf0462418bb57d8f4e9512e235cb08d6d9..7bbe97b17510c38c218a7f68743e1dd7600d4bf7 100644
--- a/sky/sdk/example/rendering/interactive_flex.dart
+++ b/sky/sdk/example/rendering/interactive_flex.dart
@@ -5,6 +5,7 @@
 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';
@@ -45,6 +46,9 @@ void handleEvent(event) {
       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() {