Make the popup menu animation correct

sky/examples/stocks2/lib/stock_arrow.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 'package:sky/framework/fn2.dart';
 import 'package:vector_math/vector_math.dart';
 import 'package:sky/framework/rendering/box.dart';
 import 'package:sky/framework/rendering/object.dart';
 import 'package:sky/framework/theme2/colors.dart' as colors;
 
@@ skipping 14 matching lines @@
 
   Color _colorForPercentChange(double percentChange) {
     if (percentChange > 0)
       return colors.Green[_colorIndexForPercentChange(percentChange)];
     return colors.Red[_colorIndexForPercentChange(percentChange)];
   }
 
   UINode build() {
     // TODO(jackson): This should change colors with the theme
     Color color = _colorForPercentChange(percentChange);
-    const double size = 40.0;
-    var arrow = new CustomPaint(callback: (sky.Canvas canvas) {
+    const double kSize = 40.0;
+    var arrow = new CustomPaint(callback: (sky.Canvas canvas, Size size) {
       Paint paint = new Paint()..color = color;
       paint.strokeWidth = 1.0;
       var padding = paint.strokeWidth * 3.0;
-      var r = size / 2.0 - padding;
+      var r = kSize / 2.0 - padding;
       canvas.save();
       canvas.translate(padding, padding);
 
       // The arrow (below) is drawn upwards by default.
       if (percentChange < 0.0) {
         canvas.translate(r, r);
         canvas.rotate(math.PI);
         canvas.translate(-r, -r);
       }
 
@@ skipping 10 matching lines @@
 
       // Draw a circle that circumscribes the arrow.
       paint.setStyle(sky.PaintingStyle.stroke);
       canvas.drawCircle(r, r, r + 2.0, paint);
 
       canvas.restore();
     });
 
     return new Container(
         child: arrow,
-        width: size,
-        height: size,
+        width: kSize,
+        height: kSize,
         margin: const EdgeDims.symmetric(horizontal: 5.0));
   }
 
 }