Add context information to driver and add hooks for plugin management

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

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 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';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(PluginInfoTest);
     defineReflectiveTests(PluginManagerTest);
     defineReflectiveTests(PluginManagerFromDiskTest);
     defineReflectiveTests(PluginSessionTest);
@@ skipping 519 matching lines @@
       void onNotification(Notification notification),
       {Function onError, void onDone()}) {
     fail('Unexpected invocation of listen');
   }
 
   @override
   void sendRequest(Request request) {
     sentRequests.add(request);
   }
 }