[Effen] Slightly cleaner enforcement of App lifetime signals

sky/framework/fn.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.
 
 library fn;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:sky' as sky;
 import 'reflect.dart' as reflect;
@@ skipping 629 matching lines @@
   if (!_buildScheduled) {
     _buildScheduled = true;
     new Future.microtask(_buildDirtyComponents);
   }
 }
 
 abstract class Component extends Node {
   bool get _isBuilding => _currentlyBuilding == this;
   bool _dirty = true;
 
+  sky.Node get _host => _root.parentNode;
+  sky.Node get _insertionPoint => _root == null ? _root : _root.nextSibling;
+
   Node _built;
   final int _order;
   static int _currentOrder = 0;
   bool _stateful;
   static Component _currentlyBuilding;
 
   Component({ Object key, bool stateful })
       : _stateful = stateful != null ? stateful : false,
         _order = _currentOrder + 1,
         super(key:key);
@@ skipping 68 matching lines @@
 
     _built = _syncChild(_built, oldBuilt, host, insertBefore);
     _dirty = false;
     _root = _built._root;
   }
 
   void _buildIfDirty() {
     if (!_dirty || _defunct)
       return;
 
-    assert(_root != null);
-    _sync(null, _root.parentNode, _root.nextSibling);
+    assert(_host != null);
+    _sync(null, _host, _insertionPoint);
   }
 
   void scheduleBuild() {
     setState(() {});
   }
 
   void setState(Function fn()) {
     _stateful = true;
     fn();
     if (_isBuilding || _dirty || _defunct)
       return;
 
     _dirty = true;
     _scheduleComponentForRender(this);
   }
 
   Node build();
 }
 
 abstract class App extends Component {
-  sky.Node _host = null;
+  sky.Node _host;
+
   App() : super(stateful: true) {
     _host = sky.document.createElement('div');
     sky.document.appendChild(_host);
-
-    new Future.microtask(() {
-      Stopwatch sw = new Stopwatch()..start();
-
-      _sync(null, _host, null);
-      assert(_root is sky.Node);
-      _notifyMountStatusChanged();
-
-      sw.stop();
-      if (_shouldLogRenderDuration)
-        print("Initial build: ${sw.elapsedMicroseconds} microseconds");
-    });
+    _scheduleComponentForRender(this);
   }
 }