big update to observe, template_binding, polymer

pkg/observe/lib/html.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // TODO(jmesserly): can we handle this more elegantly?
 // In general, it seems like we want a convenient way to take a Stream plus a
 // getter and convert this into an Observable.
 
 /** Helpers for exposing dart:html as observable data. */
 library observe.html;
@@ skipping 33 matching lines @@
     _notifyHashChange(null);
   }
 
   void _notifyHashChange(_) {
     var oldValue = _currentHash;
     _currentHash = hash;
     notifyPropertyChange(#hash, oldValue, _currentHash);
   }
 }
 
-/** Add or remove CSS class [className] based on the [value]. */
+/**
+ * *Deprecated* use [CssClassSet.toggle] instead.
+ *
+ * Add or remove CSS class [className] based on the [value].
+ */
+@deprecated
 void updateCssClass(Element element, String className, bool value) {
   if (value == true) {
     element.classes.add(className);
   } else {
     element.classes.remove(className);
   }
 }
 
-/** Bind a CSS class to the observable [object] and property [path]. */
+/**
+ * *Deprecated* use `class="{{ binding }}"` in your HTML instead. It will also
+ * work on a `<polymer-element>`.
+ *
+ * Bind a CSS class to the observable [object] and property [path].
+ */
+@deprecated
 PathObserver bindCssClass(Element element, String className,
     Observable object, String path) {
 
-  return new PathObserver(object, path)..bindSync((value) {
+  callback(value) {
     updateCssClass(element, className, value);
-  });
+  }
+
+  var obs = new PathObserver(object, path);
+  callback(obs.open(callback));
+  return obs;
 }