Add context information to driver and add hooks for plugin management

pkg/analysis_server/test/src/plugin/plugin_manager_test.dart

Index: pkg/analysis_server/test/src/plugin/plugin_manager_test.dart
diff --git a/pkg/analysis_server/test/src/plugin/plugin_manager_test.dart b/pkg/analysis_server/test/src/plugin/plugin_manager_test.dart
index 57b0c7dacef83ce8373bbacfced1346c626cc154..917c3f86e90599fd784c8348c32ba658610f1562 100644
--- a/pkg/analysis_server/test/src/plugin/plugin_manager_test.dart
+++ b/pkg/analysis_server/test/src/plugin/plugin_manager_test.dart
@@ -7,12 +7,14 @@ import 'dart:io' as io;
 
 import 'package:analysis_server/src/plugin/notification_manager.dart';
 import 'package:analysis_server/src/plugin/plugin_manager.dart';
+import 'package:analyzer/context/context_root.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
 import 'package:analyzer_plugin/channel/channel.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
-import 'package:analyzer_plugin/protocol/protocol_generated.dart';
+import 'package:analyzer_plugin/protocol/protocol_generated.dart'
+    hide ContextRoot;
 import 'package:path/path.dart' as path;
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';