Avoid repeating common parts of ProgramResults.

dart/tests/try/poi/library_updater_test.dart

 // Copyright (c) 2014, 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.
 
-// Test of LibraryUpdater.
+// Test of LibraryUpdater (one compilation unit per library).
 library trydart.library_updater_test;
 
 import 'dart:convert' show
     UTF8;
 
 import 'package:dart2js_incremental/library_updater.dart' show
     IncrementalCompilerContext,
     LibraryUpdater,
     Update;
 
@@ skipping 105 matching lines @@
           new LibraryUpdaterTestCase(
               before: 'main() => null;',
               after: 'main() {}',
               canReuse: true,
               updates: ['main']),
 
           // TODO(ahe): When supporting class members, test abstract methods.
       ]
   );
 }