Roll Observatory packages and add a roll script

packages/dart_style/lib/src/line_writer.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.line_writer;
 
 import 'chunk.dart';
 import 'dart_formatter.dart';
 import 'debug.dart' as debug;
 import 'line_splitting/line_splitter.dart';
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   final int selectionStart;
 
   /// Where in the resulting buffer the selection end point should appear if it
   /// was contained within this split list of chunks.
   ///
   /// Otherwise, this is `null`.
   final int selectionEnd;
 
   FormatResult(this.text, this.cost, this.selectionStart, this.selectionEnd);
 }