Update to use the latest version of the plugin package

pkg/analysis_server/lib/src/provisional/completion/dart/completion_plugin.dart

 // Copyright (c) 2015, 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 analysis_server.src.provisional.completion.dart.plugin;
 
 import 'package:analysis_server/src/provisional/completion/completion.dart';
 import 'package:analysis_server/src/provisional/completion/dart/completion.dart';
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/arglist_contributor.dart';
@@ skipping 32 matching lines @@
 
   /**
    * The unique identifier of this plugin.
    */
   static const String UNIQUE_IDENTIFIER = 'dart.completion';
 
   /**
    * The extension point that allows plugins to register Dart specific
    * completion contributor factories.
    */
-  ExtensionPoint _contributorExtensionPoint;
+  ExtensionPoint<DartCompletionContributorFactory> _contributorExtensionPoint;
 
   /**
    * Return a list containing all of the Dart specific completion contributors.
    */
   Iterable<DartCompletionContributor> get contributors =>
       _contributorExtensionPoint.extensions.map(
           (Object factory) => (factory as DartCompletionContributorFactory)());
 
   @override
   String get uniqueIdentifier => UNIQUE_IDENTIFIER;
 
   @override
   void registerExtensionPoints(RegisterExtensionPoint registerExtensionPoint) {
-    _contributorExtensionPoint = registerExtensionPoint(
-        CONTRIBUTOR_EXTENSION_POINT,
-        _validateDartCompletionContributorExtension);
+    _contributorExtensionPoint =
+        new ExtensionPoint<DartCompletionContributorFactory>(
+            this, CONTRIBUTOR_EXTENSION_POINT, null);
+    registerExtensionPoint(_contributorExtensionPoint);
   }
 
   @override
   void registerExtensions(RegisterExtension registerExtension) {
     //
     // Register DartCompletionManager as a CompletionContributor
     // which delegates to all the DartCompletionContributors
     //
     registerExtension(COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
         () => new DartCompletionManager());
@@ skipping 32 matching lines @@
     //     () => new OverrideContributor());
     registerExtension(DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
         () => new StaticMemberContributor());
     registerExtension(DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
         () => new TypeMemberContributor());
     registerExtension(DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
         () => new UriContributor());
     registerExtension(DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
         () => new VariableNameContributor());
   }
-
-  /**
-   * Validate the given extension by throwing an [ExtensionError] if it is not a
-   * valid Dart specific completion contributor.
-   */
-  void _validateDartCompletionContributorExtension(Object extension) {
-    if (extension is! DartCompletionContributorFactory) {
-      String id = _contributorExtensionPoint.uniqueIdentifier;
-      throw new ExtensionError(
-          'Extensions to $id must be a DartCompletionContributorFactory');
-    }
-  }
 }