Break up another large file

pkg/analyzer/test/src/task/strong/strong_test_helper.dart

Index: pkg/analyzer/test/src/task/strong/strong_test_helper.dart
diff --git a/pkg/analyzer/test/src/task/strong/strong_test_helper.dart b/pkg/analyzer/test/src/task/strong/strong_test_helper.dart
index 5b9f89ad65b4062e8a4d6498298d4404894e5397..dd033017e86817e5e38c13c4a18d6f87db4edcf2 100644
--- a/pkg/analyzer/test/src/task/strong/strong_test_helper.dart
+++ b/pkg/analyzer/test/src/task/strong/strong_test_helper.dart
@@ -9,12 +9,14 @@ library analyzer.test.src.task.strong.strong_test_helper;
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/error/error.dart';
+import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/source/error_processor.dart';
 import 'package:analyzer/src/dart/ast/token.dart';
+import 'package:analyzer/src/error/codes.dart';
 import 'package:analyzer/src/generated/engine.dart';
-import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:source_span/source_span.dart';
 import 'package:unittest/unittest.dart';
@@ -270,6 +272,7 @@ List<LibraryElement> _reachableLibraries(LibraryElement start) {
     lib.importedLibraries.forEach(find);
     lib.exportedLibraries.forEach(find);
   }
+
   find(start);
   return results;
 }