Remove references to AnalysisDriver from the plugin mixin classes

pkg/analyzer_plugin/test/plugin/completion_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/completion_mixin.dart';
@@ skipping 68 matching lines @@
 class _TestServerPlugin extends MockServerPlugin with CompletionMixin {
   _TestServerPlugin(ResourceProvider resourceProvider)
       : super(resourceProvider);
 
   CompletionSuggestion createSuggestion() {
     return new CompletionSuggestion(
         CompletionSuggestionKind.IDENTIFIER, 1, '', 0, 0, false, false);
   }
 
   @override
-  List<CompletionContributor> getCompletionContributors(
-      AnalysisDriverGeneric driver) {
+  List<CompletionContributor> getCompletionContributors(String path) {
     return <CompletionContributor>[
       new _TestCompletionContributor(
           <CompletionSuggestion>[createSuggestion(), createSuggestion()]),
       new _TestCompletionContributor(
           <CompletionSuggestion>[createSuggestion()]),
     ];
   }
 
   @override
   Future<CompletionRequest> getCompletionRequest(
-      CompletionGetSuggestionsParams parameters,
-      covariant AnalysisDriverGeneric driver) async {
+      CompletionGetSuggestionsParams parameters) async {
     AnalysisResult result = new AnalysisResult(
         null, null, null, null, null, null, null, null, null, null, null);
     return new DartCompletionRequestImpl(
         resourceProvider, parameters.offset, result);
   }
 }