Introduce boot.js: this finally makes it possible to load and run Todomvc

lib/polymer.dart

 // Copyright (c) 2012, 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.
 
 /**
  * This library exports all of the commonly used functions and types for
  * building UI's.
  *
  * See this article for more information:
  * <http://www.dartlang.org/articles/dart-web-components/>.
  */
 library polymer;
 
+import 'dart:async';
+import 'dart:mirrors' show currentMirrorSystem;
+
+import 'package:mdv/mdv.dart' as mdv;
+import 'package:observe/observe.dart' show Observable;
+import 'polymer_element.dart' show registerPolymerElement;
+
 export 'custom_element.dart';
 export 'event.dart';
 export 'observe.dart';
+export 'package:observe/observe.dart';
 export 'observe_html.dart';
 export 'polymer_element.dart';
 export 'safe_html.dart';
 export 'scoped_css.dart';
+
+
+/** Annotation used to automatically register polymer elements. */
+class CustomTag {
+  final String tagName;
+  const CustomTag(this.tagName);
+}
+
+/** All libraries in the current isolate. */
+var _libs = currentMirrorSystem().libraries;
+
+/**
+ * Registers any [PolymerElement] in the library at [uri] that is marked
+ * with the [CustomTag] annotation.

[Jennifer Messerly, 2013/07/30 00:56:12]

did we lose support for "_init"? I'm worried a little worried about that--it
means we have less features than JS does (no place to do top-level
initialization)... I like CustomTag as sugar but it seems like it's now
required?

[Siggi Cherem (dart-lang), 2013/07/30 23:32:04]

Ok, I added it back. Now we have both options. I changed todomvc to illustrate
using both kinds of initialization.

+ */
+void _registerPolymerElementsOf(String uri) {
+  for (var c in _libs[Uri.parse(uri)].classes.values) {
+    for (var m in c.metadata) {
+      var meta = m.reflectee;
+      if (meta is CustomTag) {
+        registerPolymerElement(meta.tagName,
+            () => c.newInstance(const Symbol(''), const []).reflectee);
+      }
+    }
+  }
+}
+
+/**
+ * Initializes a polymer application by: setting up polling for observable
+ * changes, initializing MDV, registering custom eleemnts from each library in
+ * [elementLibraries], and finally invoking [userMain].
+ */
+initPolymer(List<String> elementLibraries, void userMain()) {
+  new Timer.periodic(new Duration(milliseconds: 125),
+      (_) => Observable.dirtyCheck());
+
+  // TODO(jmesserly): mdv should use initMdv instead of mdv.initialize.
+  mdv.initialize();
+  for (var lib in elementLibraries) {
+    _registerPolymerElementsOf(lib);
+  }
+  userMain();
+}