dart2js: run dartfmt on tests

tests/compiler/dart2js_extra/11673_test.dart

 // Copyright (c) 2013, 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:expect/expect.dart";
 
 // Tests codegen of methods reached only via interface implemented by mixin
 // application.
 
 class JSIB {}
+
 class TD {}
+
 class M {
   foo() => 123;
 }
+
 class I8 extends TD with M implements JSIB {}
 
 use(x) {
   if (x is JSIB) {
     // Should be able to find M.foo since I8 is a subtype of both JSIB and M.
     Expect.equals(123, x.foo());
   }
 }
 
 main() {
   (use)(new I8());
 }