dart2js: reuse stack trace on rethrow

tests/compiler/dart2js_extra/identical_trace_test.dart

 // 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.
 
 import 'package:expect/expect.dart';
 
-bool inCheckedMode() {
+main() {
+  var st1;
   try {
-    int i = 'hest';
-  } catch (e) {
-    return true;
+    try {
+      throw 'bad';
+    } catch (e, st) {
+      st1 = st;
+      rethrow;
+    }
+    Expect.fail('Exception expected');
+  } catch (e, st2) {
+    Expect.equals(st1, st2);
+    Expect.identical(st1, st2);
+    return;
   }
-  return false;
+  Expect.fail('Exception expected');
 }
-
-main() {
-  if (inCheckedMode()) {
-    Expect.throws(() { List<int> t = new List<String>(); });
-  }
-}