Roll Observatory packages and add a roll script

packages/yaml/lib/src/loader.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.loader;
 
 import 'package:charcode/ascii.dart';
 import 'package:source_span/source_span.dart';
 
 import 'equality.dart';
@@ skipping 45 matching lines @@
     var document = _loadDocument(event);
     _span = _span.expand(document.span);
     _aliases.clear();
     return document;
   }
 
   /// Composes a document object.
   YamlDocument _loadDocument(DocumentStartEvent firstEvent) {
     var contents = _loadNode(_parser.parse());
 
-    var lastEvent = _parser.parse();
+    var lastEvent = _parser.parse() as DocumentEndEvent;
     assert(lastEvent.type == EventType.DOCUMENT_END);
 
     return new YamlDocument.internal(
         contents,
         firstEvent.span.expand(lastEvent.span),
         firstEvent.versionDirective,
         firstEvent.tagDirectives,
         startImplicit: firstEvent.isImplicit,
         endImplicit: lastEvent.isImplicit);
   }
@@ skipping 43 matching lines @@
     return node;
   }
 
   /// Composes a sequence node.
   YamlNode _loadSequence(SequenceStartEvent firstEvent) {
     if (firstEvent.tag != "!" && firstEvent.tag != null &&
         firstEvent.tag != "tag:yaml.org,2002:seq") {
       throw new YamlException("Invalid tag for sequence.", firstEvent.span);
     }
 
-    var children = [];
+    var children = <YamlNode>[];
     var node = new YamlList.internal(
         children, firstEvent.span, firstEvent.style);
     _registerAnchor(firstEvent.anchor, node);
 
     var event = _parser.parse();
     while (event.type != EventType.SEQUENCE_END) {
       children.add(_loadNode(event));
       event = _parser.parse();
     }
 
@@ skipping 209 matching lines @@
         case ".nan":
         case ".NaN":
         case ".NAN":
           return double.NAN;
       }
     }
 
     return null;
   }
 }