Roll Observatory packages and add a roll script

packages/code_transformers/lib/src/entry_point.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.
 import 'dart:async';
 
 import 'package:analyzer/analyzer.dart' as analyzer;
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:barback/barback.dart';
 
 /// Checks to see if the provided AssetId is a Dart file in a directory which
@@ skipping 39 matching lines @@
 
   if (hasMain) return true;
 
   // If it has an export or a part, assume the worst- that the main could be
   // in there.
   // We avoid loading those since this can be run from isPrimaryAsset calls
   // where we do not have access to other sources.
   return compilationUnit.directives
       .any((node) => node is ExportDirective || node is PartDirective);
 }