Roll Observatory packages and add a roll script

packages/polymer/lib/default_build.dart

 // Copyright (c) 2013, 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 that defines a main which calls build() from builder.dart. For
 /// polymer projects the build.dart file can simply export this to make the
 /// linter run on all of the entry points defined in your pubspec.yaml.
 library polymer.default_build;
 
 import 'builder.dart';
 
 main(args) {
   lint(options: parseOptions(args));
 }