Roll Observatory packages and add a roll script

packages/dart_style/lib/src/call_chain_visitor.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.call_chain_visitor;
 
 import 'package:analyzer/analyzer.dart';
 
 import 'argument_list_visitor.dart';
 import 'rule/argument.dart';
@@ skipping 227 matching lines @@
   }
 
   /// Ends the span wrapping the call chain if it hasn't ended already.
   void _endSpan() {
     if (_spanEnded) return;
 
     _visitor.builder.endSpan();
     _spanEnded = true;
   }
 }