Kill onDidMount()/onDidUnmount() in favour of just overriding the relevant methods.

sky/sdk/lib/framework/components2/popup_menu.dart

Index: sky/sdk/lib/framework/components2/popup_menu.dart
diff --git a/sky/sdk/lib/framework/components2/popup_menu.dart b/sky/sdk/lib/framework/components2/popup_menu.dart
index e11a528e2f1d50771657c7af6aefa15d57b3fa8c..11cb2979b41aa65f24a2e7602302dd6d91daf3a9 100644
--- a/sky/sdk/lib/framework/components2/popup_menu.dart
+++ b/sky/sdk/lib/framework/components2/popup_menu.dart
@@ -57,7 +57,6 @@ class PopupMenu extends AnimatedComponent {
     animate(controller.position, (double value) {
       _position = value;
     });
-    // onDidMount(_measureSize);
   }
 
   PopupMenuController controller;
@@ -94,6 +93,11 @@ class PopupMenu extends AnimatedComponent {
   //     height: ${math.min(_height, _height * _position * 1.5)}px;''';
   // }
 
+  // void didMount() {
+  //   _measureSize();
+  //   super.didMount();
+  // }
+
   // void _measureSize() {
   //   setState(() {
   //     var root = getRoot();