Style guide says enum values should be lowerCamelCase.

sky/sdk/lib/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:mirrors';
 import 'dart:sky' as sky;
@@ skipping 591 matching lines @@
 
   RenderNodeWrapper get _emptyNode => _emptyContainer;
 
   final FlexDirection direction;
 
   FlexContainer({
     Object key,
     List<UINode> children,
     Style style,
     String inlineStyle,
-    this.direction: FlexDirection.Row
+    this.direction: FlexDirection.horizontal
   }) : super(
     key: key,
     children: children,
     style: style,
     inlineStyle: inlineStyle
   );
 
   void _syncRenderNode(UINode old) {
     super._syncRenderNode(old);
     _root.direction = direction;
@@ skipping 329 matching lines @@
     assert(_root.parent == _host);
   }
 }
 
 class Text extends Component {
   Text(this.data) : super(key: '*text*');
   final String data;
   bool get interchangeable => true;
   UINode build() => new Paragraph(children: [new TextFragment(data)]);
 }