Roll Observatory packages and add a roll script

packages/initialize/lib/src/initialize_tracker.dart

 // Copyright (c) 2015, 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 initialize.test.initialize_tracker;
 
 import 'package:initialize/initialize.dart';
 
 // Initializer that just saves everything it sees.
 class InitializeTracker implements Initializer<dynamic> {
   static final List seen = [];
 
   const InitializeTracker();
 
   @override
   void initialize(value) => seen.add(value);
 }
 
 const initializeTracker = const InitializeTracker();