Add native extensions to the Dart shell, on the linux platform.

tests/standalone/src/test_extension.dart

Index: tests/standalone/src/test_extension.dart
diff --git a/tests/standalone/src/test_extension.dart b/tests/standalone/src/test_extension.dart
new file mode 100644
index 0000000000000000000000000000000000000000..e36d3eb446dedf933e9879e4c07dda3561c5c934
--- /dev/null
+++ b/tests/standalone/src/test_extension.dart
@@ -0,0 +1,18 @@
+// 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.
+
+#library("test_extension");
+
+#import("dart-ext:test_extension");
+
+class Cat {
+  Cat(this.x);
+
+  num x;
+
+  String toString() => 'cat $x';
+
+  // Implements (a != null) ? a : b using a native C++ function and the API.
+  static int ifNull(a, b) native 'Cat_IfNull';
+}