Add 'startPaused' option to Isolate.spawn*.

runtime/lib/isolate_patch.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.
 
 import "dart:collection" show HashMap;
 
 patch class ReceivePort {
   /* patch */ factory ReceivePort() = _ReceivePortImpl;
 
   /* patch */ factory ReceivePort.fromRawReceivePort(RawReceivePort rawPort) =
@@ skipping 209 matching lines @@
       var entryMessage = message[1];
       entryPoint(entryMessage);
     }
   }
 
   Isolate._self.handler = isolateStartHandler;
 }
 
 patch class Isolate {
   /* patch */ static Future<Isolate> spawn(
-      void entryPoint(message), var message) {
+      void entryPoint(message), var message, { bool startPaused: false }) {
     try {
       // The VM will invoke [_startIsolate] with entryPoint as argument.
       SendPort controlPort = _spawnFunction(entryPoint);
       RawReceivePort readyPort = new RawReceivePort();
       controlPort.send([readyPort.sendPort, message]);
       Completer completer = new Completer<Isolate>.sync();
       readyPort.handler = (readyMessage) {
         assert(readyMessage == 'started');
         readyPort.close();
         completer.complete(new Isolate._fromControlPort(controlPort));
       };
       return completer.future;
     } catch (e, st) {
       return new Future<Isolate>.error(e, st);
     };
   }
 
   /* patch */ static Future<Isolate> spawnUri(
-      Uri uri, List<String> args, var message) {
+      Uri uri, List<String> args, var message, { bool startPaused: false }) {
     try {
       // The VM will invoke [_startIsolate] and not `main`.
       SendPort controlPort = _spawnUri(uri.toString());
       RawReceivePort readyPort = new RawReceivePort();
       controlPort.send([readyPort.sendPort, args, message]);
       Completer completer = new Completer<Isolate>.sync();
       readyPort.handler = (readyMessage) {
         assert(readyMessage == 'started');
         readyPort.close();
         completer.complete(new Isolate._fromControlPort(controlPort));
@@ skipping 12 matching lines @@
       native "Isolate_spawnFunction";
 
   static SendPort _spawnUri(String uri) native "Isolate_spawnUri";
 }
 
 patch class Capability {
   /* patch */ factory Capability() {
     throw new UnimplementedError();
   }
 }