fix analysis messages

lib/src/testing.dart

 // Copyright (c) 2015, 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 ddc.src.testing;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart' show TimestampedData;
 import 'package:analyzer/src/generated/source.dart';
@@ skipping 269 matching lines @@
   final UriKind uriKind;
 
   _TestSource(uri, contents)
       : uri = uri,
         contents = new TimestampedData<String>(0, contents),
         _file = new SourceFile(contents, url: uri),
         uriKind = uri.scheme == 'file' ? UriKind.FILE_URI : UriKind.PACKAGE_URI;
 
   bool exists() => true;
 
+  Source get source => this;
+
   String _encoding;
   String get encoding => _encoding != null ? _encoding : (_encoding = '$uri');
 
   String get fullName => uri.path;
 
   int get modificationStamp => 0;
   String get shortName => path.basename(uri.path);
 
   operator ==(other) => other is _TestSource && uri == other.uri;
   int get hashCode => uri.hashCode;
   bool get isInSystemLibrary => false;
 
   Uri resolveRelativeUri(Uri relativeUri) => uri.resolveUri(relativeUri);
 
   SourceSpan spanFor(AstNode node) {
     final begin = node is AnnotatedNode
         ? node.firstTokenAfterCommentAndMetadata.offset
         : node.offset;
     return _file.span(begin, node.end);
   }
 
   String toString() => '[$runtimeType: $uri]';
 }