hook new DartCompletionContributor API into existing framework

pkg/analysis_server/test/services/completion/completion_computer_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.services.completion.suggestion;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/analysis_server.dart';
@@ skipping 66 matching lines @@
 
   @override
   void tearDown() {
     _continuePerformingAnalysis = false;
   }
 
   test_compute_fastAndFull() {
     contributor1 = new MockCompletionContributor(suggestion1, null);
     contributor2 = new MockCompletionContributor(null, suggestion2);
     manager.contributors = [contributor1, contributor2];
+    manager.newContributors = [];
     int count = 0;
     bool done = false;
     AnalysisServer server = new AnalysisServerMock(searchEngine: searchEngine);
     CompletionRequest completionRequest =
         new CompletionRequestImpl(server, context, source, 0);
     manager.results(completionRequest).listen((CompletionResult r) {
       bool isLast = r is CompletionResultImpl ? r.isLast : true;
       switch (++count) {
         case 1:
           contributor1.assertCalls(context, source, 0, searchEngine);
@@ skipping 18 matching lines @@
     });
     return pumpEventQueue(250).then((_) {
       expect(done, isTrue);
     });
   }
 
   test_compute_fastOnly() {
     contributor1 = new MockCompletionContributor(suggestion1, null);
     contributor2 = new MockCompletionContributor(suggestion2, null);
     manager.contributors = [contributor1, contributor2];
+    manager.newContributors = [];
     int count = 0;
     bool done = false;
     AnalysisServer server = new AnalysisServerMock(searchEngine: searchEngine);
     CompletionRequest completionRequest =
         new CompletionRequestImpl(server, context, source, 0);
     manager.results(completionRequest).listen((CompletionResult r) {
       bool isLast = r is CompletionResultImpl ? r.isLast : true;
       switch (++count) {
         case 1:
           contributor1.assertCalls(context, source, 0, searchEngine);
@@ skipping 63 matching lines @@
   @override
   Future<bool> computeFull(DartCompletionRequest request) {
     this.request = request;
     fullCount++;
     if (fullSuggestion != null) {
       request.addSuggestion(fullSuggestion);
     }
     return new Future.value(fullSuggestion != null);
   }
 }