Fix native extension lookup

tests/standalone/io/test_relative_extension.dart

Index: tests/standalone/io/test_relative_extension.dart
diff --git a/tests/standalone/io/test_extension.dart b/tests/standalone/io/test_relative_extension.dart
similarity index 81%
copy from tests/standalone/io/test_extension.dart
copy to tests/standalone/io/test_relative_extension.dart
index beed87c69a39214affde6cf1bec3d2808cfbf834..79f9489c1c34b82129dcf77f4d9cb844dde77fd2 100644
--- a/tests/standalone/io/test_extension.dart
+++ b/tests/standalone/io/test_relative_extension.dart
@@ -1,10 +1,10 @@
-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2016, 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 test_extension;
 
-import "dart-ext:test_extension";
+import "dart-ext:extension/test_extension";
 
 class Cat {
   Cat(this.x);