Provide stdout and stderr output in the Observatory debugger.

runtime/vm/service/vmservice.dart

 // Copyright (c) 2013, 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 vmservice;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:isolate';
 import 'dart:typed_data';
@@ skipping 160 matching lines @@
   }
 
   String _encodeResult(Message message, Map result) {
     var response = {
       'id' : message.serial,
       'result' : result,
     };
     return JSON.encode(response);
   }
 
-  bool _isValidStream(String streamId) {
-    final validStreams = [ 'Isolate', 'Debug', 'GC', '_Echo', '_Graph' ];
-    return validStreams.contains(streamId);
-  }
-
   bool _isAnyClientSubscribed(String streamId) {
     for (var client in clients) {
       if (client.streams.contains(streamId)) {
         return true;
       }
     }
     return false;
   }
 
   Future<String> _streamListen(Message message) async {
     var client = message.client;
     var streamId = message.params['streamId'];
 
-    if (!_isValidStream(streamId)) {
-      return _encodeError(
-          message, _kInvalidParams,
-          details:"streamListen: invalid 'streamId' parameter: ${streamId}");
-    }
     if (client.streams.contains(streamId)) {
       return _encodeError(message, _kStreamAlreadySubscribed);
     }
     if (!_isAnyClientSubscribed(streamId)) {
-      _vmListenStream(streamId);
+      if (!_vmListenStream(streamId)) {
+        return _encodeError(
+            message, _kInvalidParams,
+            details:"streamListen: invalid 'streamId' parameter: ${streamId}");
+      }
     }
     client.streams.add(streamId);
 
     var result = { 'type' : 'Success' };
     return _encodeResult(message, result);
   }
 
   Future<String> _streamCancel(Message message) async {
     var client = message.client;
     var streamId = message.params['streamId'];
 
-    if (!_isValidStream(streamId)) {
-      return _encodeError(
-          message, _kInvalidParams,
-          details:"streamCancel: invalid 'streamId' parameter: ${streamId}");
-    }
     if (!client.streams.contains(streamId)) {
       return _encodeError(message, _kStreamNotSubscribed);
     }
     client.streams.remove(streamId);
     if (!_isAnyClientSubscribed(streamId)) {
       _vmCancelStream(streamId);
     }
 
     var result = { 'type' : 'Success' };
     return _encodeResult(message, result);
@@ skipping 89 matching lines @@
 
 void _registerIsolate(int port_id, SendPort sp, String name) {
   var service = new VMService();
   service.runningIsolates.isolateStartup(port_id, sp, name);
 }
 
 void _onStart() native "VMService_OnStart";
 
 void _onExit() native "VMService_OnExit";
 
-void _vmListenStream(String streamId) native "VMService_ListenStream";
+bool _vmListenStream(String streamId) native "VMService_ListenStream";
 
 void _vmCancelStream(String streamId) native "VMService_CancelStream";