Add StackTrace.fromString constructor.

sdk/lib/isolate/isolate.dart

 // 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.
 
 /**
  * Concurrent programming using _isolates_:
  * independent workers that are similar to threads
  * but don't share memory,
  * communicating only via messages.
  */
@@ skipping 354 matching lines @@
   /**
    * Requests that uncaught errors of the isolate are sent back to [port].
    *
    * WARNING: This method is experimental and not handled on every platform yet.
    *
    * The errors are sent back as two elements lists.
    * The first element is a `String` representation of the error, usually
    * created by calling `toString` on the error.
    * The second element is a `String` representation of an accompanying
    * stack trace, or `null` if no stack trace was provided.
+   * To convert this back to a [StackTrace] object, use [StackTrace.fromString].
    *
    * Listening using the same port more than once does nothing. It will only
    * get each error once.
    */
   external void addErrorListener(SendPort port);
 
   /**
    * Stop listening for uncaught errors through [port].
    *
    * WARNING: This method is experimental and not handled on every platform yet.
@@ skipping 215 matching lines @@
  * Description of an error from another isolate.
  *
  * This error has the same `toString()` and `stackTrace.toString()` behavior
  * as the original error, but has no other features of the original error.
  */
 class RemoteError implements Error {
   final String _description;
   final StackTrace stackTrace;
   RemoteError(String description, String stackDescription)
       : _description = description,
-        stackTrace = new _RemoteStackTrace(stackDescription);
+        stackTrace = new StackTrace.fromString(stackDescription);
   String toString() => _description;
 }
-
-class _RemoteStackTrace implements StackTrace {
-  String _trace;
-  _RemoteStackTrace(this._trace);
-  String toString() => _trace;
-}