Added support for skipping redundant dart2js compilations.

tests/standalone/io/skipping_dart2js_compilations_helper.dart

Index: tests/standalone/io/skipping_dart2js_compilations_helper.dart
diff --git a/tests/compiler/dart2js_extra/regress/4434_test.dart b/tests/standalone/io/skipping_dart2js_compilations_helper.dart
similarity index 65%
copy from tests/compiler/dart2js_extra/regress/4434_test.dart
copy to tests/standalone/io/skipping_dart2js_compilations_helper.dart
index 0f23991ee3f1d7ec5da12b50a40d1ebea6459e4b..1728e3a700d7c1317b1b151a5f70c1fa697a3e82 100644
--- a/tests/compiler/dart2js_extra/regress/4434_test.dart
+++ b/tests/standalone/io/skipping_dart2js_compilations_helper.dart
@@ -2,13 +2,10 @@
 // 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 lib_b;
-
-import '4434_lib.dart';
-
-class B extends A { }
+import 'dart:io';
 
 main() {
-  B b = new B();
-  b.x(b);
+  var outputFile = new Options().arguments[0];
+  var file = new File(outputFile);
+  file.createSync();
 }