Roll Observatory packages and add a roll script

usage/lib/usage_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.
-
-/**
- * In order to use this library import the `usage_html.dart` file and
- * instantiate the [AnalyticsHtml] class.
- *
- * You'll need to provide a Google Analytics tracking ID, the application name,
- * and the application version.
- */
-library usage_html;
-
-import 'dart:html';
-
-import 'src/usage_impl.dart';
-import 'src/usage_impl_html.dart';
-
-export 'usage.dart';
-
-/**
- * An interface to a Google Analytics session, suitable for use in web apps.
- */
-class AnalyticsHtml extends AnalyticsImpl {
-  AnalyticsHtml(String trackingId, String applicationName, String applicationVersion) :
-    super(
-      trackingId,
-      new HtmlPersistentProperties(applicationName),
-      new HtmlPostHandler(),
-      applicationName: applicationName,
-      applicationVersion: applicationVersion) {
-    int screenWidth = window.screen.width;
-    int screenHeight = window.screen.height;
-
-    setSessionValue('sr', '${screenWidth}x$screenHeight');
-    setSessionValue('sd', '${window.screen.pixelDepth}-bits');
-    setSessionValue('ul', window.navigator.language);
-  }
-}