Roll Observatory packages and add a roll script

usage/lib/src/usage_impl_html.dart

-// Copyright (c) 2014, 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.
-
-library usage_impl_html;
-
-import 'dart:async';
-import 'dart:convert' show JSON;
-import 'dart:html';
-
-import 'usage_impl.dart';
-
-class HtmlPostHandler extends PostHandler {
-  final Function mockRequestor;
-
-  HtmlPostHandler({Function this.mockRequestor});
-
-  Future sendPost(String url, Map<String, String> parameters) {
-    int viewportWidth = document.documentElement.clientWidth;
-    int viewportHeight = document.documentElement.clientHeight;
-
-    parameters['vp'] = '${viewportWidth}x$viewportHeight';
-
-    String data = postEncode(parameters);
-    var request = mockRequestor == null ? HttpRequest.request : mockRequestor;
-    return request(url, method: 'POST', sendData: data).catchError((e) {
-      // Catch errors that can happen during a request, but that we can't do
-      // anything about, e.g. a missing internet conenction.
-    });
-  }
-}
-
-class HtmlPersistentProperties extends PersistentProperties {
-  Map _map;
-
-  HtmlPersistentProperties(String name) : super(name) {
-    String str = window.localStorage[name];
-    if (str == null || str.isEmpty) str = '{}';
-    _map = JSON.decode(str);
-  }
-
-  dynamic operator[](String key) => _map[key];
-
-  void operator[]=(String key, dynamic value) {
-    if (value == null) {
-      _map.remove(key);
-    } else {
-      _map[key] = value;
-    }
-
-    window.localStorage[name] = JSON.encode(_map);
-  }
-}