Roll Observatory packages and add a roll script

yaml/lib/src/yaml_document.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.yaml_document;
-
-import 'dart:collection';
-
-import 'package:source_span/source_span.dart';
-
-import 'yaml_node.dart';
-
-/// A YAML document, complete with metadata.
-class YamlDocument {
-  /// The contents of the document.
-  final YamlNode contents;
-
-  /// The span covering the entire document.
-  final SourceSpan span;
-
-  /// The version directive for the document, if any.
-  final VersionDirective versionDirective;
-
-  /// The tag directives for the document.
-  final List<TagDirective> tagDirectives;
-
-  /// Whether the beginning of the document was implicit (versus explicit via
-  /// `===`).
-  final bool startImplicit;
-
-  /// Whether the end of the document was implicit (versus explicit via `...`).
-  final bool endImplicit;
-
-  /// Users of the library should not use this constructor.
-  YamlDocument.internal(this.contents, this.span, this.versionDirective,
-          List<TagDirective> tagDirectives, {this.startImplicit: false,
-          this.endImplicit: false})
-      : tagDirectives = new UnmodifiableListView(tagDirectives);
-
-  String toString() => contents.toString();
-}
-
-/// A directive indicating which version of YAML a document was written to.
-class VersionDirective {
-  /// The major version number.
-  final int major;
-
-  /// The minor version number.
-  final int minor;
-
-  VersionDirective(this.major, this.minor);
-
-  String toString() => "%YAML $major.$minor";
-}
-
-/// A directive describing a custom tag handle.
-class TagDirective {
-  /// The handle for use in the document.
-  final String handle;
-
-  /// The prefix that the handle maps to.
-  final String prefix;
-
-  TagDirective(this.handle, this.prefix);
-
-  String toString() => "%TAG $handle $prefix";
-}