move polymer.dart into dart svn

pkg/polymer/lib/observe_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 polymer.observe_html;
+
+import 'dart:html';
+import 'package:observe/observe.dart';
+
+/** An observable version of [window.location.hash]. */
+final ObservableLocationHash windowLocation = new ObservableLocationHash._();
+
+class ObservableLocationHash extends ChangeNotifierBase {
+  ObservableLocationHash._() {
+    // listen on changes to #hash in the URL
+    // Note: listen on both popState and hashChange, because IE9 doesn't support
+    // history API. See http://dartbug.com/5483
+    // TODO(jmesserly): only listen to these if someone is listening to our
+    // changes.
+    window.onHashChange.listen(_notifyHashChange);
+    window.onPopState.listen(_notifyHashChange);
+  }
+
+  String get hash => window.location.hash;
+
+  /**
+   * Pushes a new URL state, similar to the affect of clicking a link.
+   * Has no effect if the [value] already equals [window.location.hash].
+   */
+  void set hash(String value) {
+    if (value == hash) return;
+
+    window.history.pushState(null, '', value);
+    _notifyHashChange(null);
+  }
+
+  void _notifyHashChange(_) {
+    notifyChange(new PropertyChangeRecord(const Symbol('hash')));
+  }
+}
+
+/** Add or remove CSS class [className] based on the [value]. */
+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]. */
+PathObserver bindCssClass(Element element, String className,
+    Observable object, String path) {
+
+  return new PathObserver(object, path)..bindSync((value) {
+    updateCssClass(element, className, value);
+  });
+}