Add support for specifying files needing analysis

pkg/analysis_server/test/edit/assists_test.dart

Index: pkg/analysis_server/test/edit/assists_test.dart
diff --git a/pkg/analysis_server/test/edit/assists_test.dart b/pkg/analysis_server/test/edit/assists_test.dart
index 35174166e6de651813945a0ce2cffeb4b38a4bd1..42ca88a619e527059eacbdb71304ad1fc1937d27 100644
--- a/pkg/analysis_server/test/edit/assists_test.dart
+++ b/pkg/analysis_server/test/edit/assists_test.dart
@@ -7,7 +7,6 @@ library test.edit.assists;
 import 'dart:async';
 
 import 'package:analysis_server/src/edit/edit_domain.dart';
-import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:analysis_server/src/protocol.dart';
 import 'package:plugin/manager.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
@@ -42,9 +41,8 @@ class AssistsTest extends AbstractAnalysisTest {
     super.setUp();
     createProject();
     ExtensionManager manager = new ExtensionManager();
-    ServerPlugin plugin = new ServerPlugin();
-    manager.processPlugins([plugin]);
-    handler = new EditDomainHandler(server, plugin);
+    manager.processPlugins([server.serverPlugin]);
+    handler = new EditDomainHandler(server);
   }
 
   Future test_removeTypeAnnotation() async {