[Effen] Port fn.dart from the legacy sky.Node backend to the RenderNode backend, which is currently…

sky/framework/components/popup_menu.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.
 
 import 'animated_component.dart';
 import '../animation/animated_value.dart';
 import '../fn.dart';
 import '../theme/colors.dart';
 import 'dart:async';
 import 'dart:math' as math;
@@ skipping 74 matching lines @@
       return null;
     return '''
       opacity: ${math.min(1.0, _position * 3.0)};
       width: ${math.min(_width, _width * (0.5 + _position * 2.0))}px;
       height: ${math.min(_height, _height * _position * 1.5)}px;''';
   }
 
   void _measureSize() {
     setState(() {
       var root = getRoot();
-      _width = root.clientWidth;
-      _height = root.clientHeight;
+      _width = root.width.round();
+      _height = root.height.round();
     });
   }
 
   UINode build() {
     int i = 0;
     List<UINode> children = new List.from(items.map((List<UINode> item) {
       double opacity = _opacityFor(i);
       return new PopupMenuItem(key: i++, children: item, opacity: opacity);
     }));
 
     return new Material(
       content: new Container(
         style: _style,
         inlineStyle: _inlineStyle(),
         children: children
       ),
       level: level);
   }
 }