Roll Observatory packages and add a roll script

packages/yaml/lib/src/scanner.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 yaml.scanner;
 
 import 'package:collection/collection.dart';
 import 'package:string_scanner/string_scanner.dart';
 import 'package:source_span/source_span.dart';
 
@@ skipping 425 matching lines @@
         }
         return;
       case COLON:
         if (!_inBlockContext && _tokens.isNotEmpty) {
           // If a colon follows a "JSON-like" value (an explicit map or list, or
           // a quoted string) it isn't required to have whitespace after it
           // since it unambiguously describes a map.
           var token = _tokens.last;
           if (token.type == TokenType.FLOW_SEQUENCE_END ||
               token.type == TokenType.FLOW_MAPPING_END ||
-              (token.type == TokenType.SCALAR && token.style.isQuoted)) {
+              (token.type == TokenType.SCALAR &&
+                  (token as ScalarToken).style.isQuoted)) {
             _fetchValue();
             return;
           }
         }
 
         if (_isPlainCharAt(1)) {
           _fetchPlainScalar();
         } else {
           _fetchValue();
         }
@@ skipping 1217 matching lines @@
 
   /// All trailing whitespace is preserved.
   static const KEEP = const _Chomping("KEEP");
 
   final String name;
 
   const _Chomping(this.name);
 
   String toString() => name;
 }