Support for show/hide combinators

tests/language/import1_lib.dart

Index: tests/language/import1_lib.dart
===================================================================
--- tests/language/import1_lib.dart	(revision 0)
+++ tests/language/import1_lib.dart	(revision 0)
@@ -0,0 +1,19 @@
+// 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 import1_lib;
+
+
+int libfunc(a, b) => a + b;
+
+var show = 'show';
+var hide = 'hide';
+
+var ugly = 'ugly';
+
+class Q {
+  var _s;
+  Q(s) : _s = s;
+  toString() => "LQQK: '$_s'";
+}