rework ArgListContributor to use new task model

pkg/analysis_server/lib/src/services/completion/dart_completion_manager.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 services.completion.dart;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/provisional/completion/completion_core.dart'
     show AnalysisRequest, CompletionContributor, CompletionRequest;
 import 'package:analysis_server/src/provisional/completion/dart/completion_target.dart';
-import 'package:analysis_server/src/services/completion/arglist_contributor.dart';
 import 'package:analysis_server/src/services/completion/combinator_contributor.dart';
 import 'package:analysis_server/src/services/completion/completion_core.dart';
 import 'package:analysis_server/src/services/completion/completion_manager.dart';
 import 'package:analysis_server/src/services/completion/dart/common_usage_sorter.dart';
 import 'package:analysis_server/src/services/completion/dart/contribution_sorter.dart';
 import 'package:analysis_server/src/services/completion/dart_completion_cache.dart';
 import 'package:analysis_server/src/services/completion/imported_reference_contributor.dart';
 import 'package:analysis_server/src/services/completion/local_reference_contributor.dart';
 import 'package:analysis_server/src/services/completion/optype.dart';
 import 'package:analysis_server/src/services/completion/prefixed_element_contributor.dart';
@@ skipping 69 matching lines @@
       [this.contributors, this.newContributors, this.contributionSorter])
       : super(context, source) {
     if (contributors == null) {
       contributors = [
         // LocalReferenceContributor before ImportedReferenceContributor
         // because local suggestions take precedence
         // and can hide other suggestions with the same name
         new LocalReferenceContributor(),
         new ImportedReferenceContributor(),
         //new KeywordContributor(),
-        new ArgListContributor(),
+        //new ArgListContributor(),
         new CombinatorContributor(),
         new PrefixedElementContributor(),
         new UriContributor(),
         // TODO(brianwilkerson) Use the completion contributor extension point
         // to add the contributor below (and eventually, all the contributors).
 //        new NewCompletionWrapper(new InheritedContributor())
       ];
     }
     if (newContributors == null) {
-      newContributors = <CompletionContributor>[
-        // TODO(danrubel) initialize using plugin API
-        //new newImpl.DartCompletionManager(),
-      ];
+      newContributors = <CompletionContributor>[];
     }
     if (contributionSorter == null) {
       contributionSorter = defaultContributionSorter;
     }
   }
 
   /**
    * Create a new initialized Dart source completion manager
    */
   factory DartCompletionManager.create(
@@ skipping 321 matching lines @@
             parameterNames: suggestion.parameterNames,
             parameterTypes: suggestion.parameterTypes,
             requiredParameterCount: suggestion.requiredParameterCount,
             hasNamedParameters: suggestion.hasNamedParameters,
             returnType: suggestion.returnType,
             element: suggestion.element);
       }
     }
   }
 }