fix #136, support watch exprs and two way bindings for component fields

lib/web_components.dart

Index: lib/web_components.dart
diff --git a/lib/web_components.dart b/lib/web_components.dart
index 45071302c987a8e64072cf46ef01ccadd3e4c502..66f21a9ba8a9da42b6a3e4556936d8994443ada7 100644
--- a/lib/web_components.dart
+++ b/lib/web_components.dart
@@ -266,6 +266,8 @@ abstract class WebComponent implements Element {
 
   // TODO(jmesserly): this forwarding is temporary until Dart supports
   // subclassing Elements.
+  // TODO(jmesserly): we were missing the setter for title, are other things
+  // missing setters?
 
   List<Node> get nodes => _element.nodes;
 
@@ -361,6 +363,8 @@ abstract class WebComponent implements Element {
 
   String get title => _element.title;
 
+  set title(String value) { _element.title = value; }
+
   bool get translate => _element.translate;
 
   String get webkitdropzone => _element.webkitdropzone;