Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/source_span/src/colors.dart

Index: observatory_pub_packages/source_span/src/colors.dart
===================================================================
--- observatory_pub_packages/source_span/src/colors.dart	(revision 0)
+++ observatory_pub_packages/source_span/src/colors.dart	(working copy)
@@ -0,0 +1,13 @@
+// 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.
+
+// Color constants used for generating messages.
+library source_span.colors;
+
+const String RED = '\u001b[31m';
+
+const String YELLOW = '\u001b[33m';
+
+const String NONE = '\u001b[0m';
+