Style guide says enum values should be lowerCamelCase.

sky/examples/raw/interactive_flex.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 'dart:sky';
 import 'dart:math' as math;
 import 'package:sky/framework/net/image_cache.dart' as image_cache;
 import 'package:sky/framework/app.dart';
 import 'package:sky/framework/rendering/box.dart';
 import 'package:sky/framework/rendering/block.dart';
@@ skipping 35 matching lines @@
   }
 }
 
 void main() {
   void addFlexChildSolidColor(RenderFlex parent, Color backgroundColor, { int flex: 0 }) {
     RenderSolidColorBox child = new RenderSolidColorBox(backgroundColor);
     parent.add(child);
     child.parentData.flex = flex;
   }
 
-  var row = new RenderFlex(direction: FlexDirection.Horizontal);
+  var row = new RenderFlex(direction: FlexDirection.horizontal);
 
   // Left cell
   addFlexChildSolidColor(row, const Color(0xFF00D2B8), flex: 1);
 
   // Resizeable image
   image = new RenderImageGrow("https://www.dartlang.org/logos/dart-logo.png",
                               new Size(100.0, null));
   var padding = new RenderPadding(padding: const EdgeDims.all(10.0), child: image);
   row.add(padding);
 
-  RenderFlex column = new RenderFlex(direction: FlexDirection.Vertical);
+  RenderFlex column = new RenderFlex(direction: FlexDirection.vertical);
 
   // Top cell
   addFlexChildSolidColor(column, const Color(0xFF55DDCA), flex: 1);
 
   // The internet is a beautiful place.  https://baconipsum.com/
   String meatyString = """Bacon ipsum dolor amet ham fatback tri-tip, prosciutto
 porchetta bacon kevin meatball meatloaf pig beef ribs chicken. Brisket ribeye
 andouille leberkas capicola meatloaf. Chicken pig ball tip pork picanha bresaola
 alcatra. Pork pork belly alcatra, flank chuck drumstick biltong doner jowl.
 Pancetta meatball tongue tenderloin rump tail jowl boudin.""";
   RenderParagraph paragraph = new RenderParagraph(text: meatyString, color: const Color(0xFF009900));
   padding = new RenderPadding(padding: const EdgeDims.all(10.0), child: paragraph);
   column.add(padding);
 
   // Bottom cell
   addFlexChildSolidColor(column, const Color(0xFF0081C6), flex: 2);
 
   row.add(column);
   column.parentData.flex = 8;
 
   RenderDecoratedBox root = new RenderDecoratedBox(
     decoration: new BoxDecoration(backgroundColor: const Color(0xFFFFFFFF)),
     child: row
   );
 
   app = new AppView(root);
   view.setEventCallback(handleEvent);
 }