implement dirty checking for @observable objects

pkg/mdv/lib/src/element.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.
 
 part of mdv;
 
 /** Extensions to the [Element] API. */
 class _ElementExtension extends _NodeExtension {
   _ElementExtension(Element node) : super(node);
 
@@ skipping 25 matching lines @@
     } else {
       changed = (value) {
         // TODO(jmesserly): escape value if needed to protect against XSS.
         // See https://github.com/polymer-project/mdv/issues/58
         node.xtag.attributes[name] = value == null ? '' : '$value';
       };
     }
 
     unbind(name);
 
-    _attributeBindings[name] =
-        new PathObserver(model, path).bindSync(changed);
+    _attributeBindings[name] = new PathObserver(model, path).bindSync(changed);
   }
 
   void unbind(String name) {
     if (_attributeBindings != null) {
       var binding = _attributeBindings.remove(name);
       if (binding != null) binding.cancel();
     }
   }
 
   void unbindAll() {
     if (_attributeBindings != null) {
       for (var binding in _attributeBindings.values) {
         binding.cancel();
       }
       _attributeBindings = null;
     }
   }
 }