[Effen] use the fact that the parent knows its depth already to avoid walking the entire tree each …

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 57 matching lines @@
 
 /*
  * All Effen nodes derive from UINode. All nodes have a _parent, a _key and
  * can be sync'd.
  */
 abstract class UINode {
   String _key;
   UINode _parent;
   sky.Node _root;
   bool _defunct = false;
-  int _nodeDepth;
 
   UINode({ Object key }) {
     _key = key == null ? "$runtimeType" : "$runtimeType-$key";
   }
 
   // Subclasses which implements Nodes that become stateful may return true
   // if the |old| node has become stateful and should be retained.
   bool _willSync(UINode old) => false;
 
   void _sync(UINode old, sky.ParentNode host, sky.Node insertBefore);
 
   void _remove() {
     _defunct = true;
     _root = null;
   }
 
+  int _nodeDepth;
   void _ensureDepth() {
     if (_nodeDepth == null) {
-      _nodeDepth = 0;
-      UINode parent = _parent;
-      while (parent != null) {
-        _nodeDepth++;
-        parent = parent._parent;
-      }
+      _parent.ensureDepth();
+      _nodeDepth = _parent._nodeDepth + 1;
     }
   }
 
   void _trace(String message) {
     if (!_shouldTrace)
       return;
 
     _ensureDepth();
-    StringBuffer buffer = new StringBuffer();
-    int depth = _nodeDepth;
-    while (depth-- > 0) {
-      buffer.write(' ');
-    }
-    buffer.write(message);
-    print(buffer);
+    print((' ' * _nodeDepth) + message);
   }
 
   void _traceSync(_SyncOperation op, String key) {
     if (!_shouldTrace)
       return;
 
     String opString = op.toString().toLowerCase();
     String outString = opString.substring(opString.indexOf('.') + 1);
     _trace('_sync($outString) $key');
   }
@@ skipping 771 matching lines @@
 
 abstract class App extends Component {
   sky.Node _host;
 
   App() : super(stateful: true) {
     _host = sky.document.createElement('div');
     sky.document.appendChild(_host);
     _scheduleComponentForRender(this);
   }
 }