Use new task model in completion tests [TBR].

pkg/analysis_server/test/domain_completion_test.dart

 // Copyright (c) 2014, 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.
 
 library test.domain.completion;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/analysis_server.dart';
@@ skipping 36 matching lines @@
 }
 
 @reflectiveTest
 class CompletionManagerTest extends AbstractAnalysisTest {
   AnalysisDomainHandler analysisDomain;
   Test_CompletionDomainHandler completionDomain;
   Request request;
   int requestCount = 0;
   String testFile2 = '/project/bin/test2.dart';
 
+  /// Cached model state in case tests need to set task model to on/off.
+  bool wasTaskModelEnabled;
+
   AnalysisServer createAnalysisServer(Index index) {
     ExtensionManager manager = new ExtensionManager();
     ServerPlugin serverPlugin = new ServerPlugin();
     manager.processPlugins([serverPlugin]);
     return new Test_AnalysisServer(
         super.serverChannel,
         super.resourceProvider,
         super.packageMapProvider,
         index,
         serverPlugin,
@@ skipping 10 matching lines @@
   void sendRequest(String path) {
     String id = (++requestCount).toString();
     request = new CompletionGetSuggestionsParams(path, 0).toRequest(id);
     Response response = handler.handleRequest(request);
     expect(response, isResponseSuccess(id));
   }
 
   @override
   void setUp() {
     super.setUp();
+    wasTaskModelEnabled = AnalysisEngine.instance.useTaskModel;
+    AnalysisEngine.instance.useTaskModel = true;
     createProject();
     analysisDomain = handler;
     completionDomain = new Test_CompletionDomainHandler(server);
     handler = completionDomain;
     addTestFile('^library A; cl');
     addFile(testFile2, 'library B; cl');
   }
 
   void tearDown() {
     super.tearDown();
     analysisDomain = null;
     completionDomain = null;
+    AnalysisEngine.instance.useTaskModel = wasTaskModelEnabled;
   }
 
   /**
    * Assert different managers are used for different sources
    */
   test_2_requests_different_sources() {
     expect(completionDomain.manager, isNull);
     sendRequest(testFile);
     expect(completionDomain.manager, isNotNull);
     MockCompletionManager expectedManager = completionDomain.manager;
@@ skipping 730 matching lines @@
 }
     ''');
     await waitForTasksFinished();
     Request request =
         new CompletionGetSuggestionsParams(testFile, 0).toRequest('0');
     Response response = handler.handleRequest(request);
     expect(response.error, isNotNull);
     expect(response.error.code, RequestErrorCode.NO_INDEX_GENERATED);
   }
 }