Update the plugin API

pkg/analyzer_plugin/test/utilities/completion/completion_contributor_util.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/source/package_map_resolver.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer/src/generated/source.dart';
@@ skipping 14 matching lines @@
 }
 
 abstract class DartCompletionContributorTest extends AbstractContextTest {
   static const String _UNCHECKED = '__UNCHECKED__';
   String testFile;
   Source testSource;
   int completionOffset;
   int replacementOffset;
   int replacementLength;
   CompletionContributor contributor;
-  CompletionRequest request;
+  DartCompletionRequest request;
   List<CompletionSuggestion> suggestions;
 
   /**
    * If `true` and `null` is specified as the suggestion's expected returnType
    * then the actual suggestion is expected to have a `dynamic` returnType.
    * Newer tests return `false` so that they can distinguish between
    * `dynamic` and `null`.
    * Eventually all tests should be converted and this getter removed.
    */
   bool get isNullExpectedReturnTypeConsideredDynamic => true;
@@ skipping 514 matching lines @@
     addSource(path, content);
   }
 
   @override
   void setUp() {
     super.setUp();
     testFile = provider.convertPath('/completionTest.dart');
     contributor = createContributor();
   }
 }