Roll Observatory packages and add a roll script

packages/usage/example/ga.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.
+
+/**
+ * A simple command-line app to hand-test the usage library.
+ */
+library usage_ga;
+
+import 'package:usage/usage_io.dart';
+
+void main(List args) {
+  final String DEFAULT_UA = 'UA-55029513-1';
+
+  if (args.isEmpty) {
+    print('usage: dart ga <GA tracking ID>');
+    print('pinging default UA value (${DEFAULT_UA})');
+  } else {
+    print('pinging ${args.first}');
+  }
+
+  String ua = args.isEmpty ? DEFAULT_UA : args.first;
+
+  Analytics ga = new AnalyticsIO(ua, 'ga_test', '1.0');
+  ga.optIn = true;
+
+  ga.sendScreenView('home').then((_) {
+    return ga.sendScreenView('files');
+  }).then((_) {
+    return ga.sendException('foo exception, line 123:56');
+  }).then((_) {
+    return ga.sendTiming('writeDuration', 123);
+  }).then((_) {
+    return ga.sendEvent('create', 'consoleapp', label: 'Console App');
+  }).then((_) {
+    print('pinged ${ua}');
+  });
+}