Adds PID to `server.connected` notification (#26744).

pkg/analysis_server/lib/src/analysis_server.dart

Index: pkg/analysis_server/lib/src/analysis_server.dart
diff --git a/pkg/analysis_server/lib/src/analysis_server.dart b/pkg/analysis_server/lib/src/analysis_server.dart
index 6a87e4bbb327e1242c8f2537503715a13be972bc..be9f995d6a34268b5c391481b673451924b8738e 100644
--- a/pkg/analysis_server/lib/src/analysis_server.dart
+++ b/pkg/analysis_server/lib/src/analysis_server.dart
@@ -7,6 +7,7 @@ library analysis.server;
 import 'dart:async';
 import 'dart:collection';
 import 'dart:core' hide Resource;
+import 'dart:io' as io;
 import 'dart:math' show max;
 
 import 'package:analysis_server/plugin/protocol/protocol.dart'
@@ -364,8 +365,9 @@ class AnalysisServer {
       });
     });
     _setupIndexInvalidation();
+    String pid = io.pid.toString();
     Notification notification =
-        new ServerConnectedParams(VERSION).toNotification();
+        new ServerConnectedParams(VERSION, pid).toNotification();
     channel.sendNotification(notification);
     channel.listen(handleRequest, onDone: done, onError: error);
     handlers = serverPlugin.createDomains(this);