Clean up some Dart idioms in fn

sky/examples/fn/lib/node.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.
+
 part of fn;
 
-void parentInsertBefore(sky.ParentNode parent,
-                        sky.Node node,
-                        sky.Node ref) {
+void _parentInsertBefore(sky.ParentNode parent,
+                         sky.Node node,
+                         sky.Node ref) {
   if (ref != null) {
     ref.insertBefore([node]);
   } else {
     parent.appendChild(node);
   }
 }
 
 abstract class Node {
   String _key = null;
   sky.Node _root = null;
@@ skipping 18 matching lines @@
 
   // Text nodes are special cases of having non-unique keys (which don't need
   // to be assigned as part of the API). Since they are unique in not having
   // children, there's little point to reordering, so we always just re-assign
   // the data.
   Text(this.data) : super(key:'*text*');
 
   bool _sync(Node old, sky.ParentNode host, sky.Node insertBefore) {
     if (old == null) {
       _root = new sky.Text(data);
-      parentInsertBefore(host, _root, insertBefore);
+      _parentInsertBefore(host, _root, insertBefore);
       return false;
     }
 
     _root = old._root;
     (_root as sky.Text).data = data;
     return false;
   }
 }
 
-var _emptyList = new List<Node>();
+final List<Node> _emptyList = new List<Node>();
 
 abstract class Element extends Node {
 
   String get _tagName;
 
   Element get _emptyElement;
 
   String inlineStyle;
 
   sky.EventListener onClick;
@@ skipping 30 matching lines @@
     this.onPointerUp,
     this.onScrollEnd,
     this.onScrollStart,
     this.onScrollUpdate,
     this.onWheel
   }) : super(key:key) {
 
     _className = style == null ? '': style._className;
     _children = children == null ? _emptyList : children;
 
-    if (debugWarnings()) {
+    if (_debugWarnings()) {
       _debugReportDuplicateIds();
     }
   }
 
   void _remove() {
     super._remove();
     if (_children != null) {
       for (var child in _children) {
         child._remove();
       }
@@ skipping 71 matching lines @@
       // print("...no oldElement, initial render");
 
       _root = sky.document.createElement(_tagName);
       _syncNode();
 
       for (var child in _children) {
         child._sync(null, _root, null);
         assert(child._root is sky.Node);
       }
 
-      parentInsertBefore(host, _root, insertBefore);
+      _parentInsertBefore(host, _root, insertBefore);
       return false;
     }
 
     _root = oldElement._root;
     oldElement._root = null;
     sky.Element root = (_root as sky.Element);
 
     _syncNode(oldElement);
 
     var startIndex = 0;
@@ skipping 68 matching lines @@
       if (currentNode is Text)
         return false; // Never re-order Text nodes.
 
       ensureOldIdMap();
       oldNode = oldNodeIdMap[currentNode._key];
       if (oldNode == null)
         return false;
 
       oldNodeIdMap[currentNode._key] = null; // mark it reordered.
       // print("Reparenting ${currentNode._key}");
-      parentInsertBefore(root, oldNode._root, nextSibling);
+      _parentInsertBefore(root, oldNode._root, nextSibling);
       return true;
     }
 
     // Scan forwards, this time we may re-order;
     // print("...scanning forward");
     nextSibling = root.firstChild;
     while (startIndex < endIndex && oldStartIndex < oldEndIndex) {
       currentNode = _children[startIndex];
       oldNode = oldChildren[oldStartIndex];
 
@@ skipping 40 matching lines @@
 
     oldElement._children = null;
     return false;
   }
 }
 
 class Container extends Element {
 
   String get _tagName => 'div';
 
-  static Container _emptyContainer = new Container();
+  static final Container _emptyContainer = new Container();
 
   Element get _emptyElement => _emptyContainer;
 
   Container({
     Object key,
     List<Node> children,
     Style style,
     String inlineStyle,
     sky.EventListener onClick,
     sky.EventListener onFlingCancel,
@@ skipping 24 matching lines @@
     onScrollStart: onScrollStart,
     onScrollUpdate: onScrollUpdate,
     onWheel: onWheel
   );
 }
 
 class Image extends Element {
 
   String get _tagName => 'img';
 
-  static Image _emptyImage = new Image();
+  static final Image _emptyImage = new Image();
   Element get _emptyElement => _emptyImage;
 
   String src;
   int width;
   int height;
 
   Image({
     Object key,
     List<Node> children,
     Style style,
@@ skipping 47 matching lines @@
     if (height != oldImage.height) {
       skyImage.style['height'] = '${height}px';
     }
   }
 }
 
 class Anchor extends Element {
 
   String get _tagName => 'a';
 
-  static Anchor _emptyAnchor = new Anchor();
+  static final Anchor _emptyAnchor = new Anchor();
 
   String href;
 
   Anchor({
     Object key,
     List<Node> children,
     Style style,
     String inlineStyle,
     sky.EventListener onClick,
     sky.EventListener onFlingCancel,
@@ skipping 32 matching lines @@
   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;
     }
   }
 }