dart2js: run dartfmt on tests

tests/compiler/dart2js_extra/lookup_map/subclass_lookup_map_test.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.
 
 import 'package:lookup_map/lookup_map.dart';
 import 'package:expect/expect.dart';
-class A{}
-class B{}
+
+class A {}
+
+class B {}
+
 class S extends LookupMap {
   const S(list) : super(list);
 }
+
 const map = const S(const [
-    A, "the-text-for-A",
-    B, "the-text-for-B",
+  A,
+  "the-text-for-A",
+  B,
+  "the-text-for-B",
 ]);
 
 main() {
   Expect.equals(map[A], "the-text-for-A");
 }