Remove references to AnalysisDriver from the plugin mixin classes

pkg/analyzer_plugin/lib/plugin/assist_mixin.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/dart/analysis/results.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/plugin/plugin.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
 import 'package:analyzer_plugin/protocol/protocol_generated.dart';
 import 'package:analyzer_plugin/src/utilities/assist/assist.dart';
 import 'package:analyzer_plugin/utilities/assist/assist.dart';
 import 'package:analyzer_plugin/utilities/generator.dart';
 
 /**
  * A mixin that can be used when creating a subclass of [ServerPlugin] to
  * provide most of the implementation for handling assist requests.
  *
  * Clients may not extend or implement this class, but are allowed to use it as
  * a mix-in when creating a subclass of [ServerPlugin].
  */
 abstract class AssistsMixin implements ServerPlugin {
   /**
    * Return a list containing the assist contributors that should be used to
-   * create assists when used in the context of the given analysis [driver].
+   * create assists for the file with the given [path].
    */
-  List<AssistContributor> getAssistContributors(
-      covariant AnalysisDriverGeneric driver);
+  List<AssistContributor> getAssistContributors(String path);
 
   /**
    * Return the assist request that should be passes to the contributors
    * returned from [getAssistContributors].
    */
-  Future<AssistRequest> getAssistRequest(
-      EditGetAssistsParams parameters, covariant AnalysisDriverGeneric driver);
+  Future<AssistRequest> getAssistRequest(EditGetAssistsParams parameters);
 
   @override
   Future<EditGetAssistsResult> handleEditGetAssists(
       EditGetAssistsParams parameters) async {
     String path = parameters.file;
-    ContextRoot contextRoot = contextRootContaining(path);
-    if (contextRoot == null) {
-      // Return an error from the request.
-      throw new RequestFailure(
-          RequestErrorFactory.pluginError('Failed to analyze $path', null));
-    }
-    AnalysisDriverGeneric driver = driverMap[contextRoot];
-    AssistRequest request = await getAssistRequest(parameters, driver);
+    AssistRequest request = await getAssistRequest(parameters);
     AssistGenerator generator =
-        new AssistGenerator(getAssistContributors(driver));
+        new AssistGenerator(getAssistContributors(path));
     GeneratorResult result = await generator.generateAssistsResponse(request);
     result.sendNotifications(channel);
     return result.result;
   }
 }
 
 /**
  * A mixin that can be used when creating a subclass of [ServerPlugin] and
  * mixing in [AssistsMixin]. This implements the creation of the assists request
  * based on the assumption that the driver being created is an [AnalysisDriver].
  *
  * Clients may not extend or implement this class, but are allowed to use it as
  * a mix-in when creating a subclass of [ServerPlugin] that also uses
  * [AssistsMixin] as a mix-in.
  */
 abstract class DartAssistsMixin implements AssistsMixin {
   @override
   Future<AssistRequest> getAssistRequest(
-      EditGetAssistsParams parameters, covariant AnalysisDriver driver) async {
-    ResolveResult result = await driver.getResult(parameters.file);
+      EditGetAssistsParams parameters) async {
+    String path = parameters.file;
+    AnalysisDriver driver = driverForPath(path);
+    if (driver == null) {
+      // Return an error from the request.
+      throw new RequestFailure(
+          RequestErrorFactory.pluginError('Failed to analyze $path', null));
+    }
+    ResolveResult result = await driver.getResult(path);
     return new DartAssistRequestImpl(
         resourceProvider, parameters.offset, parameters.length, result);
   }
 }