Create a new AstFactory class to be used by analyzer and its clients.

pkg/analyzer/lib/src/dart/ast/uri_validation_code.dart

+// Copyright (c) 2016, 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.
+
+import 'package:analyzer/dart/ast/ast.dart';
+
+/**
+ * Validation codes returned by [UriBasedDirective.validate].
+ */
+class UriValidationCodeImpl implements UriValidationCode {

[Brian Wilkerson, 2016/11/23 15:58:18]

I would prefer to remove the method 'validate' from UriBasedDirective and to
remove UriValidationCode from the public API. 

[Paul Berry, 2016/11/24 15:03:17]

Done.

+  static const UriValidationCode INVALID_URI =
+      const UriValidationCodeImpl('INVALID_URI');
+
+  static const UriValidationCode URI_WITH_INTERPOLATION =
+      const UriValidationCodeImpl('URI_WITH_INTERPOLATION');
+
+  static const UriValidationCode URI_WITH_DART_EXT_SCHEME =
+      const UriValidationCodeImpl('URI_WITH_DART_EXT_SCHEME');
+
+  /**
+   * The name of the validation code.
+   */
+  final String name;
+
+  /**
+   * Initialize a newly created validation code to have the given [name].
+   */
+  const UriValidationCodeImpl(this.name);
+
+  @override
+  String toString() => name;
+}