Roll Observatory packages and add a roll script

packages/analyzer/lib/src/string_source.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 analyzer.string_source;
 
 import 'generated/engine.dart' show TimestampedData;
 import 'generated/source.dart';
 
 /// An implementation of [Source] that's based on an in-memory Dart string.
@@ skipping 30 matching lines @@
       return ssObject._contents == _contents && ssObject.fullName == fullName;
     }
     return false;
   }
 
   bool exists() => true;
 
   Uri resolveRelativeUri(Uri relativeUri) => throw new UnsupportedError(
       "StringSource doesn't support resolveRelative.");
 }