Remove references to AnalysisDriver from the plugin mixin classes

pkg/analyzer_plugin/test/plugin/assist_mixin_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 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/plugin/assist_mixin.dart';
@@ skipping 61 matching lines @@
 
 class _TestServerPlugin extends MockServerPlugin with AssistsMixin {
   _TestServerPlugin(ResourceProvider resourceProvider)
       : super(resourceProvider);
 
   PrioritizedSourceChange createChange() {
     return new PrioritizedSourceChange(0, new SourceChange(''));
   }
 
   @override
-  List<AssistContributor> getAssistContributors(AnalysisDriverGeneric driver) {
+  List<AssistContributor> getAssistContributors(String path) {
     return <AssistContributor>[
       new _TestAssistContributor(<PrioritizedSourceChange>[createChange()]),
       new _TestAssistContributor(
           <PrioritizedSourceChange>[createChange(), createChange()])
     ];
   }
 
   @override
   Future<AssistRequest> getAssistRequest(
-      EditGetAssistsParams parameters, covariant AnalysisDriver driver) async {
+      EditGetAssistsParams parameters) async {
     AnalysisResult result = new AnalysisResult(
         null, null, null, null, null, null, null, null, null, null, null);
     return new DartAssistRequestImpl(
         resourceProvider, parameters.offset, parameters.length, result);
   }
 }