anchor.diff:  
   RenderImageGrow image;
   
  +void handleEvent(String eventType, double timeStamp) {
  +  if (eventType == "back")
  +    activity.finishCurrentActivity();
  +}
  +
   final Map<int, Touch> touches = <int, Touch>{};
  -void handleEvent(event) {
  -  if (event is ui.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 handlePointerPacket(ByteData serializedPacket) {
  +  bindings.Message message = new bindings.Message(
  +    serializedPacket,
  +    <core.MojoHandle>[]
  +  );
  +  PointerPacket packet = PointerPacket.deserialize(message);
  +
  +  for (Pointer pointer in packet.pointers) {
  +    if (pointer.type == PointerType.MOVE)
  +      image.growth = math.max(0.0, image.growth + pointer.x - touches[pointer.pointer].x);
  +    touches[pointer.pointer] = new Touch(pointer.x, pointer.y);
     }
   }
   
  
positive.code: 
  import 'dart:ui' as ui;
  import 'dart:math' as math;
  
  import 'package:flutter/services.dart';
  import 'package:flutter/rendering.dart';
  
  import 'lib/solid_color_box.dart';
  
  
negative.code:   updateTaskDescription('Interactive Flex', topColor);
    new FlutterBinding(root: root);
    ui.window.onEvent = handleEvent;
    ui.window.onPointerPacket = handlePointerPacket;
  }
  