Fix the App code to use the new names for AppView.

sky/sdk/lib/widgets/widget.dart

Index: sky/sdk/lib/widgets/widget.dart
diff --git a/sky/sdk/lib/widgets/widget.dart b/sky/sdk/lib/widgets/widget.dart
index 8eb781f473d052a0b8dceea9ecea691f0c6037d8..0773cd5ec13177dc58e4ba02853e0179857abaed 100644
--- a/sky/sdk/lib/widgets/widget.dart
+++ b/sky/sdk/lib/widgets/widget.dart
@@ -820,12 +820,12 @@ abstract class App extends Component {
 
   void didMount() {
     super.didMount();
-    WidgetAppView.appView.addEventListener(_handleEvent);
+    SkyBinding.instance.addEventListener(_handleEvent);
   }
 
   void didUnmount() {
     super.didUnmount();
-    WidgetAppView.appView.removeEventListener(_handleEvent);
+    SkyBinding.instance.removeEventListener(_handleEvent);
   }
 
   // Override this to handle back button behavior in your app