[Layout] Put in some guards to prevent us from reintroducing 'display' properties into the CSS.

sky/framework/layout.dart

 library layout;
 
 import 'node.dart';
 import 'dart:sky' as sky;
 import 'dart:collection';
 
 // UTILS
 
 // Bridge to legacy CSS-like style specification
 // Eventually we'll replace this with something else
 class Style {
   final String _className;
   static final Map<String, Style> _cache = new HashMap<String, Style>();
 
   static int _nextStyleId = 1;
 
   static String _getNextClassName() { return "style${_nextStyleId++}"; }
 
   Style extend(Style other) {
     var className = "$_className ${other._className}";
 
     return _cache.putIfAbsent(className, () {
-      return new Style._internal(className);
+      return new Style._construct(className);
     });
   }
 
   factory Style(String styles) {
+    assert(!styles.contains(new RegExp('\\b(display|flex|flex-direction)\\b')));
+    return new Style._addToCache(styles);
+  }
+
+  factory Style._addToCache(String styles) {
     return _cache.putIfAbsent(styles, () {
       var className = _getNextClassName();
       sky.Element styleNode = sky.document.createElement('style');
       styleNode.setChild(new sky.Text(".$className { $styles }"));
       sky.document.appendChild(styleNode);
-      return new Style._internal(className);
+      return new Style._construct(className);
     });
   }
 
-  Style._internal(this._className);
+  Style._construct(this._className);
 }
 
 class Rect {
   const Rect(this.x, this.y, this.width, this.height);
   final double x;
   final double y;
   final double width;
   final double height;
 }
 
@@ skipping 214 matching lines @@
   }
 
   String stylesToClasses(List<Style> styles) {
     return styles.map((s) => s._className).join(' ');
   }
 
   String _inlineStyles = '';
   String _additionalStylesFromParent = ''; // used internally to propagate parentData settings to the child
 
   void updateInlineStyle(String newStyle) {
+    assert(newStyle == null || !newStyle.contains(new RegExp('\\b(display|flex|flex-direction)\\b')));
     _inlineStyles = newStyle != null ? newStyle : '';
     _updateInlineStyleAttribute();
   }
 
   void _updateInlineStyleAttribute() {
     if ((_inlineStyles != '') && (_additionalStylesFromParent != ''))
       _skyElement.setAttribute('style', "$_inlineStyles;$_additionalStylesFromParent");
     else
       _skyElement.setAttribute('style', "$_inlineStyles$_additionalStylesFromParent");
   }
@@ skipping 73 matching lines @@
   void set direction (FlexDirection value) {
     _direction = value;
     markNeedsLayout();
   }
 
   void setupPos(RenderNode child) {
     if (child.parentData is! FlexBoxParentData)
       child.parentData = new FlexBoxParentData();
   }
 
-  static final Style _displayFlex = new Style('display:flex');
-  static final Style _displayFlexRow = new Style('flex-direction:row');
-  static final Style _displayFlexColumn = new Style('flex-direction:column');
+  static final Style _displayFlex = new Style._addToCache('display:flex');
+  static final Style _displayFlexRow = new Style._addToCache('flex-direction:row');
+  static final Style _displayFlexColumn = new Style._addToCache('flex-direction:column');
 
   String stylesToClasses(List<Style> styles) {
     var settings = _displayFlex._className;
     switch (_direction) {
       case FlexDirection.Row: settings += ' ' + _displayFlexRow._className; break;
       case FlexDirection.Column: settings += ' ' + _displayFlexColumn._className; break;
     }
     return super.stylesToClasses(styles) + ' ' + settings;
   }
 
@@ skipping 11 matching lines @@
       child = child.parentData.nextSibling;
     }
   }
 
 }
 
 class RenderCSSParagraph extends RenderCSSContainer {
 
   RenderCSSParagraph(debug) : super(debug);
 
-  static final Style _displayParagraph = new Style('display:paragraph');
+  static final Style _displayParagraph = new Style._addToCache('display:paragraph');
 
   String stylesToClasses(List<Style> styles) {
     return super.stylesToClasses(styles) + ' ' + _displayParagraph._className;
   }
 
 }
 
 class RenderCSSInline extends RenderCSS {
 
   RenderCSSInline(debug, String newData) : super(debug) {
     data = newData;
   }
 
-  static final Style _displayInline = new Style('display:inline');
+  static final Style _displayInline = new Style._addToCache('display:inline');
 
   String stylesToClasses(List<Style> styles) {
     return super.stylesToClasses(styles) + ' ' + _displayInline._className;
   }
 
   sky.Element createSkyElement() {
     return sky.document.createElement('div')
                       ..setChild(new sky.Text())
                       ..setAttribute('debug', debug.toString());
   }
@@ skipping 64 matching lines @@
   print(prefix + node.toString() + _attributes(node));
   var children = node.getChildNodes();
   prefix = prefix + '  ';
   for (var child in children)
     _serialiseDOM(child, prefix);
 }
 
 void dumpState() {
   _serialiseDOM(sky.document);
 }