SkyView should handle screen rotation

sky/sdk/lib/framework/app.dart

Index: sky/sdk/lib/framework/app.dart
diff --git a/sky/sdk/lib/framework/app.dart b/sky/sdk/lib/framework/app.dart
index 2c84da438bff732c9b54c89fb83cf4d54d32cfb7..ce27dde89552171dc72475f9f05b6a13742b5f04 100644
--- a/sky/sdk/lib/framework/app.dart
+++ b/sky/sdk/lib/framework/app.dart
@@ -18,19 +18,21 @@ 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;
@@ -56,6 +58,10 @@ class AppView {
     }
   }
 
+  void _handleMetricsChanged() {
+    _renderView.rootConstraints = _viewConstraints;
+  }
+
   PointerState _createStateForPointer(sky.PointerEvent event, Point position) {
     HitTestResult result = new HitTestResult();
     _renderView.hitTest(result, position: position);