Rework service extensions to be safe

sdk/lib/developer/extension.dart

 // Copyright (c) 2015, 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.
 
 part of dart.developer;
 
 class ServiceExtensionResponse {
   final String _result;
   final int _errorCode;
   final String _errorDetail;
@@ skipping 84 matching lines @@
     throw new ArgumentError('Extension already registered: $method');
   }
   if (handler is! ServiceExtensionHandler) {
     throw new ArgumentError.value(handler,
                                   'handler',
                                   'Must be a ServiceExtensionHandler');
   }
   _extensions[method] = handler;
 }
 
-bool _scheduleExtension(String method,
-                        List<String> parameterKeys,
-                        List<String> parameterValues,
-                        SendPort replyPort,
-                        Object id) {
+Function _scheduleExtension(String method,
+                            List<String> parameterKeys,
+                            List<String> parameterValues,
+                            SendPort replyPort,
+                            Object id) {
   ServiceExtensionHandler handler = _extensions[method];
   if (handler == null) {
-    return false;
+    return null;
   }
-  // Defer execution of handler until next event loop.
-  Timer.run(() {
+  // This closure will be executed at the next turn of the event loop.
+  return () {
     var parameters = {};
     for (var i = 0; i < parameterKeys.length; i++) {
       parameters[parameterKeys[i]] = parameterValues[i];
     }
     var response;
     try {
       response = handler(method, parameters);
     } catch (e, st) {
       var errorDetails = (st == null) ? '$e' : '$e\n$st';
       response = new ServiceExtensionResponse.error(
@@ skipping 15 matching lines @@
           ServiceExtensionResponse.kExtensionError,
           errorDetails);
     }).then((response) {
       if (response == null) {
         response = new ServiceExtensionResponse.error(
             ServiceExtensionResponse.kExtensionError,
             "Extension handler returned null");
       }
       _postResponse(replyPort, id, response);
     });
-  });
-  return true;
+  };
 }
 
 _postResponse(SendPort replyPort,
               Object id,
               ServiceExtensionResponse response) {
   assert(replyPort != null);
   if (id == null) {
     // No id -> no response.
     replyPort.send(null);
     return;
   }
   assert(id != null);
   StringBuffer sb = new StringBuffer();
   sb.write('{"jsonrpc":"2.0",');
   if (response._isError()) {
     sb.write('"error":');
   } else {
     sb.write('"result":');
   }
   sb.write('${response._toString()},');
   if (id is String) {
     sb.write('"id":"$id"}');
   } else {
     sb.write('"id":$id}');
   }
   replyPort.send(sb.toString());
 }