Add pause methods to Isolate.

tests/isolate/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:async_helper/async_helper.dart";
+
+isomain1(replyPort) {
+  RawReceivePort port = new RawReceivePort();
+  port.handler = (v) {
+    replyPort.send(v);
+    port.close();
+  };
+  replyPort.send(port.sendPort);
+}
+
+main(){
+  asyncStart();
+  RawReceivePort reply = new RawReceivePort();
+  Isolate isolate;
+  Capability resume;
+  var completer = new Completer();  // Completed by first reply from isolate.
+  reply.handler = completer.complete;
+  Isolate.spawn(isomain1, reply.sendPort).then((Isolate iso) {
+    isolate = iso;
+    resume = isolate.pause();
+    return completer.future;
+  }).then((echoPort) {
+    // Isolate has been created, and first response has been returned.
+    echoPort.send(24);
+    reply.handler = (v) {
+      throw "RESPONSE WHILE PAUSED?!?";
+    };
+    return new Future.delayed(const Duration(milliseconds: 250));
+  }).then((_) {
+    reply.handler = (v) {
+      if (v != 24) throw "WRONG ANSWER!";
+      reply.close();
+      asyncEnd();
+    };
+    isolate.resume(resume);
+  });
+}