SkyView should handle screen rotation

sky/sdk/lib/framework/app.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;
 
 class PointerState {
   HitTestResult result;
   Point lastPosition;
 
   PointerState({ this.result, this.lastPosition });
 }
 
 class AppView {
 
   AppView(RenderBox root) {
     sky.view.setEventCallback(_handleEvent);
+    sky.view.setMetricsChangedCallback(_handleMetricsChanged);
     scheduler.init();
     scheduler.addPersistentFrameCallback(_beginFrame);
 
     _renderView = new RenderView(child: root);
     _renderView.attach();
-    _renderView.layout(new ViewConstraints(width: sky.view.width,
-                                           height: sky.view.height));
-
-    scheduler.ensureVisualUpdate();
+    _renderView.rootConstraints = _viewConstraints;
+    _renderView.layout(_renderView.rootConstraints);
   }
 
   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;
 
   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);
     }
   }
 
+  void _handleMetricsChanged() {
+    _renderView.rootConstraints = _viewConstraints;
+  }
+
   PointerState _createStateForPointer(sky.PointerEvent event, Point position) {
     HitTestResult result = new HitTestResult();
     _renderView.hitTest(result, position: position);
     PointerState state = new PointerState(result: result, lastPosition: position);
     _stateForPointer[event.pointer] = state;
     return state;
   }
 
   void _handlePointerEvent(sky.PointerEvent event) {
     Point position = new Point(event.x, event.y);
@@ skipping 28 matching lines @@
       node.handleEvent(event);
   }
 
   String toString() => 'Render Tree:\n${_renderView}';
 
   void debugDumpRenderTree() {
     toString().split('\n').forEach(print);
   }
   
 }