Refactor Navigator to put state in separate class, initial back button plumbing

sky/sdk/lib/app/view.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' as sky;
 
 import '../rendering/box.dart';
 import '../rendering/object.dart';
 import 'scheduler.dart' as scheduler;
 
@@ skipping 32 matching lines @@
 
   RenderView _renderView;
 
   ViewConstraints get _viewConstraints =>
       new ViewConstraints(width: sky.view.width, height: sky.view.height);
 
   Map<int, PointerState> _stateForPointer = new Map<int, PointerState>();
 
   Function onFrame;
 
+  List<sky.EventListener> eventListeners = new List<sky.EventListener>();

[Hixie, 2015/06/17 19:29:43]

Make this final, at least.

But ideally, we'd have an interface here where you can add (and remove)
listeners. Otherwise, random people can clear the list, send events to random
callbacks, etc.

Also, we shouldn't use sky.EventListener. Just use a typedef for a callback.

+
   RenderBox get root => _renderView.child;
   void set root(RenderBox value) {
     _renderView.child = value;
   }
   void _beginFrame(double timeStamp) {
     if (onFrame != null)
       onFrame();
     RenderObject.flushLayout();
     _renderView.paintFrame();
   }
 
   void _handleEvent(sky.Event event) {
     if (event is sky.PointerEvent) {
       _handlePointerEvent(event);
     } else if (event is sky.GestureEvent) {
       HitTestResult result = new HitTestResult();
       _renderView.hitTest(result, position: new Point(event.x, event.y));
       dispatchEvent(event, result);
+    } else {
+      for (sky.EventListener listener in eventListeners) {
+        listener(event);
+      }
     }
   }
 
   void _handleMetricsChanged() {
     _renderView.rootConstraints = _viewConstraints;
   }
 
   PointerState _createStateForPointer(sky.PointerEvent event, Point position) {
     HitTestResult result = new HitTestResult();
     _renderView.hitTest(result, position: position);
@@ skipping 35 matching lines @@
       entry.target.handleEvent(event, entry);
   }
 
   String toString() => 'Render Tree:\n${_renderView}';
 
   void debugDumpRenderTree() {
     toString().split('\n').forEach(print);
   }
   
 }