Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/code_transformers/src/messages.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.
+
+/// Contains all warning messages produced by the code_transformers package.
+library code_transformers.src.messages;
+
+import 'package:code_transformers/messages/messages.dart';
+
+const NO_ABSOLUTE_PATHS = const MessageTemplate(
+    const MessageId('code_transformers', 1),
+    'absolute paths not allowed: "%-url-%"',
+    'Absolute paths not allowed',
+    '''
+The transformers processing your code were trying to resolve a URL and identify
+a file that they correspond to. Currently only relative paths can be resolved.
+''');
+
+const INVALID_URL_TO_OTHER_PACKAGE = const MessageTemplate(
+    const MessageId('code_transformers', 2),
+    'Invalid URL to reach to another package: %-url-%. Path '
+    'reaching to other packages must first reach up all the '
+    'way to the %-prefix-% directory. For example, try changing the URL '
+    'to: %-fixedUrl-%',
+    'Invalid URL to reach another package',
+    '''
+To reach an asset that belongs to another package, use `package:` URLs in
+Dart code, but in any other language (like HTML or CSS) use relative URLs that
+first go all the way to the `packages/` directory.
+
+The rules for correctly writing these imports are subtle and have a lot of
+special cases. Please review
+<https://www.dartlang.org/polymer/app-directories.html> to learn
+more.
+''');
+
+const INVALID_PREFIX_PATH = const MessageTemplate(
+    const MessageId('code_transformers', 3),
+    'incomplete %-prefix-%/ path. It should have at least 3 '
+    'segments %-prefix-%/name/path_from_name\'s_%-folder-%_dir',
+    'Incomplete URL to asset in another package',
+    '''
+URLs that refer to assets in other packages need to explicitly mention the
+`packages/` directory. In the future this requirement might be removed, but for
+now you must use a canonical URL form for it.
+
+For example, if `packages/a/a.html` needs to import `packages/b/b.html`,
+you might expect a.html to import `../b/b.html`. Instead, it must import
+`../../packages/b/b.html`.
+
+See [issue 15797](http://dartbug.com/15797) and
+<https://www.dartlang.org/polymer/app-directories.html> to learn more.
+''');