Make the popup menu animation correct

sky/sdk/lib/framework/rendering/box.dart

Index: sky/sdk/lib/framework/rendering/box.dart
diff --git a/sky/sdk/lib/framework/rendering/box.dart b/sky/sdk/lib/framework/rendering/box.dart
index efbef3d22a0389e8513ed24e912b12e8e30c1590..6a8968676da24626bc4a01f09d150adaac4a6bf5 100644
--- a/sky/sdk/lib/framework/rendering/box.dart
+++ b/sky/sdk/lib/framework/rendering/box.dart
@@ -811,7 +811,7 @@ class RenderSizeObserver extends RenderProxyBox {
   }
 }
 
-typedef void CustomPaintCallback(sky.Canvas canvas);
+typedef void CustomPaintCallback(sky.Canvas canvas, Size size);
 
 class RenderCustomPaint extends RenderProxyBox {
 
@@ -839,7 +839,7 @@ class RenderCustomPaint extends RenderProxyBox {
 
   void paint(RenderObjectDisplayList canvas) {
     assert(_callback != null);
-    _callback(canvas);
+    _callback(canvas, size);
     super.paint(canvas);
   }
 }