Add a library for manipulating stack traces.

pkg/stack_trace/lib/stack_trace.dart

Index: pkg/stack_trace/lib/stack_trace.dart
diff --git a/tests/language/duplicate_interface_lib.dart b/pkg/stack_trace/lib/stack_trace.dart
similarity index 64%
copy from tests/language/duplicate_interface_lib.dart
copy to pkg/stack_trace/lib/stack_trace.dart
index 4602bcda6152b8e7e29c5e470df0751f3bf7e0e8..455dd57aea36ceca743b02df17b5082db8d20bf4 100644
--- a/tests/language/duplicate_interface_lib.dart
+++ b/pkg/stack_trace/lib/stack_trace.dart
@@ -1,11 +1,11 @@
 // Copyright (c) 2013, 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.
-// Check fail because of cycles in super class relationship.
 
-library Interface_Lib;
+library stack_trace;
 
-class InterfA { }
-
-class InterfB { }
+import 'src/trace.dart';
+import 'src/frame.dart';
 
+export 'src/trace.dart';
+export 'src/frame.dart';