Allow Effen Styles to be extendable

sky/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:sky' as sky;
 import 'reflect.dart' as reflect;
@@ skipping 28 matching lines @@
 
   void addAll(EventMap events) {
     _handlers.addAll(events._handlers);
   }
 }
 
 class Style {
   final String _className;
   static final Map<String, Style> _cache = new HashMap<String, Style>();
 
-  static int nextStyleId = 1;
+  static int _nextStyleId = 1;
 
-  static String nextClassName(String styles) {
-    assert(sky.document != null);
-    String className = "style$nextStyleId";
-    nextStyleId++;
+  static String _getNextClassName() { return "style${_nextStyleId++}"; }
 
-    sky.Element styleNode = sky.document.createElement('style');
-    styleNode.setChild(new sky.Text(".$className { $styles }"));
-    sky.document.appendChild(styleNode);
+  Style extend(Style other) {
+    var className = "$_className ${other._className}";
 
-    return className;
+    return _cache.putIfAbsent(className, () {
+      return new Style._internal(className);
+    });
   }
 
   factory Style(String styles) {
     return _cache.putIfAbsent(styles, () {
-      return new Style._internal(nextClassName(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);
     });
   }
 
   Style._internal(this._className);
 }
 
 void _parentInsertBefore(sky.ParentNode parent,
                          sky.Node node,
                          sky.Node ref) {
   if (ref != null) {
@@ skipping 57 matching lines @@
   Element get _emptyElement;
 
   String inlineStyle;
 
   List<Node> _children = null;
   String _class = '';
 
   Element({
     Object key,
     List<Node> children,
-    List<Style> styles,
+    Style style,
 
     this.inlineStyle
   }) : super(key:key) {
-    _class = styles == null ? '' : styles.map((s) => s._className).join(' ');
+    _class = style == null ? '' : style._className;
     _children = children == null ? _emptyList : children;
 
     if (_isInCheckedMode) {
       _debugReportDuplicateIds();
     }
   }
 
   void _remove() {
     super._remove();
     if (_children != null) {
@@ skipping 247 matching lines @@
 class Container extends Element {
 
   String get _tagName => 'div';
 
   static final Container _emptyContainer = new Container();
   Element get _emptyElement => _emptyContainer;
 
   Container({
     Object key,
     List<Node> children,
-    List<Style> styles,
+    Style style,
     String inlineStyle
   }) : super(
     key: key,
     children: children,
-    styles: styles,
+    style: style,
     inlineStyle: inlineStyle
   );
 }
 
 class Image extends Element {
 
   String get _tagName => 'img';
 
   static final Image _emptyImage = new Image();
   Element get _emptyElement => _emptyImage;
 
   String src;
   int width;
   int height;
 
   Image({
     Object key,
     List<Node> children,
-    List<Style> styles,
+    Style style,
     String inlineStyle,
     this.width,
     this.height,
     this.src
   }) : super(
     key: key,
     children: children,
-    styles: styles,
+    style: style,
     inlineStyle: inlineStyle
   );
 
   void _syncNode([Element old]) {
     super._syncNode(old);
 
     Image oldImage = old != null ? old : _emptyImage;
     sky.HTMLImageElement skyImage = _root as sky.HTMLImageElement;
     if (src != oldImage.src) {
       skyImage.src = src;
@@ skipping 15 matching lines @@
   static final Anchor _emptyAnchor = new Anchor();
   Element get _emptyElement => _emptyAnchor;
 
   String href;
   int width;
   int height;
 
   Anchor({
     Object key,
     List<Node> children,
-    List<Style> styles,
+    Style style,
     String inlineStyle,
     this.width,
     this.height,
     this.href
   }) : super(
     key: key,
     children: children,
-    styles: styles,
+    style: style,
     inlineStyle: inlineStyle
   );
 
   void _syncNode([Element old]) {
     Anchor oldAnchor = old != null ? old as Anchor : _emptyAnchor;
     super._syncNode(oldAnchor);
 
     sky.HTMLAnchorElement skyAnchor = _root as sky.HTMLAnchorElement;
     if (href != oldAnchor.href) {
       skyAnchor.href = href;
@@ skipping 176 matching lines @@
 
       _sync(null, _host, null);
       assert(_root is sky.Node);
 
       sw.stop();
       if (_shouldLogRenderDuration)
         print("Initial build: ${sw.elapsedMicroseconds} microseconds");
     });
   }
 }