Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/yaml/src/utils.dart

Index: observatory_pub_packages/yaml/src/utils.dart
===================================================================
--- observatory_pub_packages/yaml/src/utils.dart	(revision 0)
+++ observatory_pub_packages/yaml/src/utils.dart	(working copy)
@@ -0,0 +1,44 @@
+// Copyright (c) 2013, 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.utils;
+
+import 'package:source_span/source_span.dart';
+
+/// A pair of values.
+class Pair<E, F> {
+  final E first;
+  final F last;
+
+  Pair(this.first, this.last);
+
+  String toString() => '($first, $last)';
+}
+
+/// Print a warning.
+///
+/// If [span] is passed, associates the warning with that span.
+void warn(String message, [SourceSpan span]) =>
+    yamlWarningCallback(message, span);
+
+/// A callback for emitting a warning.
+///
+/// [message] is the text of the warning. If [span] is passed, it's the portion
+/// of the document that the warning is associated with and should be included
+/// in the printed warning.
+typedef YamlWarningCallback(String message, [SourceSpan span]);
+
+/// A callback for emitting a warning.
+///
+/// In a very few cases, the YAML spec indicates that an implementation should
+/// emit a warning. To do so, it calls this callback. The default implementation
+/// prints a message using [print].
+YamlWarningCallback yamlWarningCallback = (message, [span]) {
+  // TODO(nweiz): Print to stderr with color when issue 6943 is fixed and
+  // dart:io is available.
+  if (span != null) message = span.message(message);
+  print(message);
+};
+
+