Format all tests.

tests/language_strong/prefix2_negative_test.dart

 // Copyright (c) 2011, 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 Prefix2NegativeTest.dart;
+
 import "library2.dart" as lib2;
 
 class Prefix2NegativeTest {
   static Main() {
     // This is a syntax error as multiple prefixes are not possible.
     return lib2.Library2.main() + lib2.lib1.foo;
   }
 }
 
 main() {
   Prefix2NegativeTest.Main();
 }