Revert "Let `Isolate.errors` close on isolate exit."

sdk/lib/isolate/isolate.dart

Index: sdk/lib/isolate/isolate.dart
diff --git a/sdk/lib/isolate/isolate.dart b/sdk/lib/isolate/isolate.dart
index df7d10465785c888b929927a80f83d51975454f2..424742a15b1d47dbc07d9d6df02f2e9de88d0807 100644
--- a/sdk/lib/isolate/isolate.dart
+++ b/sdk/lib/isolate/isolate.dart
@@ -522,40 +522,25 @@ class Isolate {
    * be the same object types as in the actual isolate, but they will
    * always have the same [Object.toString] result.
    *
-   * 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
-   * stream will also not emit a done event.
-   *
-   * This stream is based on [addErrorListener], [removeErrorListener],
-   * [addOnExitListener] and [removeOnExitListener].
+   * This stream is based on [addErrorListener] and [removeErrorListener].
    */
   Stream get errors {
     StreamController controller;
     RawReceivePort port;
     void handleError(message) {
-      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();
-      }
+      String errorDescription = message[0];
+      String stackDescription = message[1];
+      var error = new RemoteError(errorDescription, stackDescription);
+      controller.addError(error, error.stackTrace);
     }
     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;
         });