Move diagnostic_listener.dart and messages.dart to the diagnostics folder

tests/compiler/dart2js/analyze_helper.dart

Index: tests/compiler/dart2js/analyze_helper.dart
diff --git a/tests/compiler/dart2js/analyze_helper.dart b/tests/compiler/dart2js/analyze_helper.dart
index 01e22ec838db7fd221c04d08e72f7f95aec44691..ccd9b3bce6dc9fcd6ad3f039421128c574ef6b60 100644
--- a/tests/compiler/dart2js/analyze_helper.dart
+++ b/tests/compiler/dart2js/analyze_helper.dart
@@ -8,9 +8,9 @@ import 'dart:async';
 import 'dart:io';
 import 'package:compiler/compiler.dart' as api;
 import 'package:compiler/src/apiimpl.dart';
-import 'package:compiler/src/filenames.dart';
-import 'package:compiler/src/messages.dart' show
+import 'package:compiler/src/diagnostics/messages.dart' show
     Message;
+import 'package:compiler/src/filenames.dart';
 import 'package:compiler/src/source_file_provider.dart';
 import 'package:compiler/src/util/uri_extras.dart';