Add Isolate ping functionality.

tests/isolate/ping_pause_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.
+
+import "dart:isolate";
+import "dart:async";
+import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
+
+isomain1(replyPort) {
+  RawReceivePort port = new RawReceivePort();
+  port.handler = (v) {
+    replyPort.send(v);
+    if (v == 0) port.close();
+  };
+  replyPort.send(port.sendPort);
+}
+
+void main() {
+  asyncStart();
+  var completer = new Completer();  // Completed by first reply from isolate.
+  RawReceivePort reply = new RawReceivePort(completer.complete);
+  Isolate.spawn(isomain1, reply.sendPort).then((Isolate isolate) {
+    List result = [];
+    completer.future.then((echoPort) {
+      reply.handler = (v) {
+        result.add(v);
+        if (v == 0) {
+          Expect.listEquals([4, 3, 2, 1, 0], result);
+          reply.close();
+          asyncEnd();
+        }
+      };
+      echoPort.send(4);
+      echoPort.send(3);
+      Capability resume = isolate.pause();
+      isolate.ping((new ReceivePort()..first.then((_) {

[floitsch, 2014/03/04 12:12:51]

I would prefer no cascading operator here.

[Lasse Reichstein Nielsen, 2014/03/06 12:47:17]

There goes the one-liner :)
Done.

+        Expect.isTrue(result.length <= 2);
+        echoPort.send(0);
+        isolate.resume(resume);
+      })).sendPort, Isolate.PING_CONTROL);
+      echoPort.send(2);
+      echoPort.send(1);
+    });
+  });
+}