workaround for event handlers: don't return StreamSubscription as model

pkg/polymer/README.md

 Polymer.dart
 ============
 
 Polymer.dart is a set of comprehensive UI and utility components
 for building web applications.
 With Polymer.dart's custom elements, templating, data binding,
 and other features,
 you can quickly build structured, encapsulated, client-side web apps.
 
 Polymer.dart is a Dart port of
@@ skipping 22 matching lines @@
 [polymer_expressions][] package,
 which provides an expressive syntax for use with templates.
 
 
 Try It Now
 -----------
 Add the polymer.dart package to your pubspec.yaml file:
 
 ```yaml
 dependencies:
-  polymer: any
+  polymer: ">=0.9.0 <0.10.0"
 ```
 
 Instead of using `any`, we recommend using version ranges to avoid getting your
 project broken on each release. Using a version range lets you upgrade your
 package at your own pace. You can find the latest version number at
 <https://pub.dartlang.org/packages/polymer>.
 
+
 Building and Deploying
 ----------------------
 
 To build a deployable version of your app, add the polymer transformers to your
 pubspec.yaml file:
 
 ```yaml
 transformers:
 - polymer
 ```
@@ skipping 55 matching lines @@
 [issues]: http://dartbug.com/new
 [mailinglist]: https://groups.google.com/a/dartlang.org/forum/?fromgroups#!forum/web-ui
 [devlist]: https://groups.google.com/a/dartlang.org/forum/?fromgroups#!forum/web-ui-dev
 [overview]: http://www.dartlang.org/articles/dart-web-components/
 [tools]: https://www.dartlang.org/articles/dart-web-components/tools.html
 [spec]: https://www.dartlang.org/articles/dart-web-components/spec.html
 [features]: https://www.dartlang.org/articles/dart-web-components/summary.html
 [home_page]: https://www.dartlang.org/polymer-dart/
 [polymer_expressions]: http://pub.dartlang.org/packages/polymer_expressions/
 [polymer]: http://www.polymer-project.org/