Port of github.com/polymer/polymer.

pkg/polymer/lib/platform.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.
+
+/**
+ * Exposes helper functionality for interacting with the platform. Similar to
+ * the [Platform] class from dart:html.
+ */
+// TODO(jmesserly): in Polymer this is a static class called "Platform", but
+// that conflicts with dart:html. What should we do? Does this functionality
+// belong in html's Platform instead?
+library polymer.platform;
+
+import 'dart:html' show Text, MutationObserver;
+import 'dart:collection' show Queue;
+import 'package:observe/src/microtask.dart' show performMicrotaskCheckpoint;
+
+void flush() {
+  endOfMicrotask(performMicrotaskCheckpoint);
+}
+
+int _iterations = 0;
+final Queue _callbacks = new Queue();
+final Text _twiddle = () {
+  var twiddle = new Text('');
+  new MutationObserver((x, y) {
+    while (_callbacks.isNotEmpty) {
+      try {
+        _callbacks.removeFirst()();
+      } catch (e) { // Dart note: fire the error async.
+        new Completer().completeError(e);
+      }
+    }
+  }).observe(twiddle, characterData: true);
+  return twiddle;
+}();
+
+void endOfMicrotask(void callback()) {
+  _twiddle.text = '${_iterations++}';
+  _callbacks.add(callback);
+}