Expose the RenderView root through the AppView, so that you can change it.

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 4c105715d9f6a9c19f4fb36d5fd23fa2ec7c1d3b..9c3815a999f71b94412609682d313ee402f9e877 100644
--- a/sky/sdk/lib/framework/app.dart
+++ b/sky/sdk/lib/framework/app.dart
@@ -12,6 +12,7 @@ class AppView {
     sky.view.setBeginFrameCallback(_beginFrame);
 
     _renderView = new RenderView(root: root);
+    _renderView.attach();
     _renderView.layout(newWidth: sky.view.width, newHeight: sky.view.height);
   
     sky.view.scheduleFrame();
@@ -19,6 +20,11 @@ class AppView {
 
   RenderView _renderView;
 
+  RenderBox get root => _renderView.root;
+  void set root(RenderBox value) {
+    _renderView.root = value;

[abarth-chromium, 2015/05/27 16:52:48]

Do we need to schedule a frame here?

[Hixie, 2015/05/27 17:41:47]

The "root" setter on RenderView takes care of that for us.

+  }
+
   void _beginFrame(double timeStamp) {
     RenderNode.flushLayout();
     _renderView.paintFrame();