Update the plugin API

pkg/analyzer_plugin/lib/plugin/completion_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';
@@ skipping 12 matching lines @@
 abstract class CompletionMixin implements ServerPlugin {
   /**
    * Return a list containing the completion contributors that should be used to
    * create completion suggestions when used in the context of the given
    * analysis [driver].
    */
   List<CompletionContributor> getCompletionContributors(
       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 completion request that should be passes to the contributors
+   * returned from [getCompletionContributors].
    */
-  Future<ResolveResult> getResolveResultForCompletion(
-      covariant AnalysisDriverGeneric driver, String path);
+  Future<CompletionRequest> getCompletionRequest(
+      CompletionGetSuggestionsParams parameters,
+      covariant AnalysisDriverGeneric driver);
 
   @override
   Future<CompletionGetSuggestionsResult> handleCompletionGetSuggestions(
       CompletionGetSuggestionsParams 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 getResolveResultForCompletion(driver, path);
-    CompletionRequestImpl request = new CompletionRequestImpl(
-        resourceProvider, analysisResult, parameters.offset);
+    CompletionRequest request = await getCompletionRequest(parameters, driver);
     CompletionGenerator generator =
         new CompletionGenerator(getCompletionContributors(driver));
     GeneratorResult result =
         await generator.generateCompletionResponse(request);
     result.sendNotifications(channel);
     return result.result;
   }
 }
+
+/**
+ * A mixin that can be used when creating a subclass of [ServerPlugin] and
+ * mixing in [CompletionMixin]. This implements the creation of the completion
+ * 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
+ * [CompletionMixin] as a mix-in.
+ */
+abstract class DartCompletionMixin implements CompletionMixin {
+  @override
+  Future<CompletionRequest> getCompletionRequest(
+      CompletionGetSuggestionsParams parameters,
+      covariant AnalysisDriver driver) async {
+    ResolveResult result = await driver.getResult(parameters.file);
+    return new DartCompletionRequestImpl(
+        resourceProvider, parameters.offset, result);
+  }
+}