Update the plugin API

pkg/analyzer_plugin/lib/plugin/fix_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/fixes/fixes.dart';
 import 'package:analyzer_plugin/utilities/fixes/fixes.dart';
 import 'package:analyzer_plugin/utilities/generator.dart';
 
 /**
+ * A mixin that can be used when creating a subclass of [ServerPlugin] and
+ * mixing in [FixesMixin]. This implements the creation of the fixes 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
+ * [FixesMixin] as a mix-in.
+ */
+abstract class DartFixesMixin implements FixesMixin {
+  @override
+  Future<FixesRequest> getFixesRequest(
+      EditGetFixesParams parameters, covariant AnalysisDriver driver) async {
+    ResolveResult analysisResult = await driver.getResult(parameters.file);
+    return new FixesRequestImpl(
+        resourceProvider, parameters.offset, analysisResult);
+  }
+}
+
+/**
  * A mixin that can be used when creating a subclass of [ServerPlugin] to
  * provide most of the implementation for handling fix 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 FixesMixin implements ServerPlugin {
   /**
    * Return a list containing the fix contributors that should be used to create
    * fixes when used in the context of the given analysis [driver].
    */
   List<FixContributor> getFixContributors(
       covariant AnalysisDriverGeneric driver);
 
   /**
-   * Return the result of using the given analysis [driver] to produce a fully
-   * resolved AST for the file with the given [path].
+   * Return the fixes request that should be passes to the contributors
+   * returned from [getFixContributors].
    */
-  Future<ResolveResult> getResolveResultForFixes(
-      covariant AnalysisDriverGeneric driver, String path);
+  Future<FixesRequest> getFixesRequest(
+      EditGetFixesParams parameters, covariant AnalysisDriverGeneric driver);
 
   @override
   Future<EditGetFixesResult> handleEditGetFixes(
       EditGetFixesParams 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];
-    ResolveResult analysisResult = await getResolveResultForFixes(driver, path);
-    FixesRequestImpl request = new FixesRequestImpl(
-        resourceProvider, parameters.offset, analysisResult);
+    FixesRequest request = await getFixesRequest(parameters, driver);
     FixGenerator generator = new FixGenerator(getFixContributors(driver));
     GeneratorResult result = await generator.generateFixesResponse(request);
     result.sendNotifications(channel);
     return result.result;
   }
 }