Roll Observatory packages and add a roll script

packages/dart_style/lib/src/formatter_exception.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.
 
 library dart_style.src.formatter_exception;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:source_span/source_span.dart';
 
 /// Thrown when one or more errors occurs while parsing the code to be
@@ skipping 33 matching lines @@
     if (shownErrors.length != errors.length) {
       buffer.writeln();
       buffer.write("(${errors.length - shownErrors.length} more errors...)");
     }
 
     return buffer.toString();
   }
 
   String toString() => message();
 }