Add an error listener on isolates.

tests/isolate/handle_error_test.dart

+// Copyright (c) 2014, 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.
+
+library handle_error_test;
+
+import "dart:isolate";
+import "dart:async";
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
+
+isomain1(replyPort) {
+  RawReceivePort port = new RawReceivePort();
+  port.handler = (v) {
+    switch (v) {
+      case 0:
+        replyPort.send(42);
+        break;
+      case 1:
+        throw new ArgumentError("whoops");
+      case 2:
+        throw new RangeError.value(37);
+      case 3:
+        port.close();
+    }
+  };
+  replyPort.send(port.sendPort);
+}
+
+main(){
+  asyncStart();
+  RawReceivePort reply = new RawReceivePort(null);
+  // Start paused so we have time to set up the error handler.
+  Isolate.spawn(isomain1, reply.sendPort, paused: true).then((Isolate isolate) {
+    isolate.setErrorsFatal(false);
+    Stream errors = isolate.errors;  // Broadcast stream, never a done message.
+    SendPort sendPort;
+    StreamSubscription subscription;
+    int state = 0;
+    reply.handler = (port) {
+      sendPort = port;
+      port.send(state);
+      reply.handler = (v) {
+        Expect.equals(0, state);
+        Expect.equals(42, v);
+        state++;
+        sendPort.send(state);
+      };
+    };
+    subscription = errors.listen(null, onError: (error, stack) {
+      switch (state) {
+        case 1:
+          Expect.equals(new ArgumentError("whoops").toString(), "$error");
+          state++;
+          sendPort.send(state);
+          break;
+        case 2:
+          Expect.equals(new RangeError.value(37).toString(), "$error");
+          state++;
+          sendPort.send(state);
+          reply.close();
+          subscription.cancel();
+          asyncEnd();
+          break;
+        default:
+          throw "Bad state for error: $state: $error";
+      }
+    });
+    isolate.resume(isolate.pauseCapability);
+  });
+}