Enable the "skip command compilation if output is already up-to-date" feature in dart2dart

tests/standalone/io/skipping_dart2js_compilations_test.dart

 // Copyright (c) 2012, 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.
 
 /*
  * This test makes sure that the "skipping Dart2Js compilations if the output is
  * already up to date" feature does work as it should.
  * Therefore this test ensures that compilations are only skipped if the last
  * modified date of the output of a dart2js compilation is newer than
  *   - the the dart application to compile (including it's dependencies)
@@ skipping 138 matching lines @@
                              TestCompletedHandler completedHandler) {
   var fileUtils = completedHandler.fileUtils;
   var config = new options.TestOptionsParser().parse(['--timeout', '2'])[0];
   var scriptDirPath = new Path.fromNative(new Options().script).directoryPath;
   var createFileScript = scriptDirPath.
       append('skipping_dart2js_compilations_helper.dart').toNativePath();
   var executable = new Options().executable;
   var arguments = [createFileScript, fileUtils.scriptOutputPath.toNativePath()];
   var bootstrapDeps = [
       new Uri("file://${fileUtils.testSnapshotFilePath}")];
-  var commands = [new runner.Dart2JsCommand(
+  var commands = [new runner.CompilationCommand(
       fileUtils.testJsFilePath.toNativePath(),
       false,
       bootstrapDeps,
       executable,
       arguments)];
   return new runner.TestCase(
       testName,
       commands,
       config,
       completedHandler.processCompletedTest,
@@ skipping 46 matching lines @@
     runTest("fs_notUpToDate_snapshot", fs_notUpToDate_snapshot, true);
     runTest("fs_notUpToDate_dart", fs_notUpToDate_dart, true);
     // This is the only test where all dependencies are present and the test.js
     // file is newer than all the others. So we pass 'false' for shouldRun.
     runTest("fs_upToDate", fs_upToDate, false);
   }
   // We need to wait some time to make sure that the files we 'touch' get a
   // bigger timestamp than the old ones
   new Timer(1000, touchFilesAndRunTests);
 }