Roll Observatory packages and add a roll script

packages/web_components/lib/src/mirror_initializer.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.
 
 /// Contains logic to initialize web_components apps during development. This
 /// implementation uses dart:mirrors to load each library as they are discovered
 /// through HTML imports. This is only meant to be used during development in
 /// dartium, and the web_components transformers replace this implementation
 /// for deployment.
 library web_components.src.mirror_initializer;
@@ skipping 177 matching lines @@
 Entry point: $entryPath
 Owner document: ${import.ownerDocument.baseUri}
 Current import: ${import.outerHtml}
 Corrected import: ${correctedImport.outerHtml}
 
 For more information, please see:
 https://www.dartlang.org/polymer/app-directories.html#into-a-non-dart-non-entry-point
 ''');
   return false;
 }