Let `Isolate.errors` close on isolate exit.

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 477 matching lines @@
 
   /**
    * Returns a broadcast stream of uncaught errors from the isolate.
    *
    * Each error is provided as an error event on the stream.
    *
    * The actual error object and stackTraces will not necessarily
    * be the same object types as in the actual isolate, but they will
    * always have the same [Object.toString] result.
    *
-   * This stream is based on [addErrorListener] and [removeErrorListener].
+   * The returned stream is done when the isolate terminates.
+   *
+   * If the isolate has already terminated, the stream will never emit
+   * any events, not even a done event.
+   * If the isolate terminates while nobody is listening, the returned

[floitsch, 2016/12/07 16:12:00]

Doesn't this sentence imply the first one?

+   * stream will also not emit a done event.
+   *
+   * This stream is based on [addErrorListener], [removeErrorListener],
+   * [addOnExitListener] and [removeOnExitListener].
    */
   Stream get errors {
     StreamController controller;
     RawReceivePort port;
     void handleError(message) {
-      String errorDescription = message[0];
-      String stackDescription = message[1];
-      var error = new RemoteError(errorDescription, stackDescription);
-      controller.addError(error, error.stackTrace);
+      if (message != null) {
+        String errorDescription = message[0];
+        String stackDescription = message[1];
+        var error = new RemoteError(errorDescription, stackDescription);
+        controller.addError(error, error.stackTrace);
+      } else {
+        port.close();
+        controller.close();
+      }
     }
     controller = new StreamController.broadcast(
         sync: true,
         onListen: () {
           port = new RawReceivePort(handleError);
+          this.addOnExitListener(port.sendPort);
           this.addErrorListener(port.sendPort);
         },
         onCancel: () {
           this.removeErrorListener(port.sendPort);
+          this.removeOnExitListener(port.sendPort);
           port.close();
           port = null;
         });
     return controller.stream;
   }
 }
 
 /**
  * Sends messages to its [ReceivePort]s.
  *
@@ skipping 143 matching lines @@
  * 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 StackTrace.fromString(stackDescription);
   String toString() => _description;
 }