Update to use the latest version of the plugin package

pkg/analyzer/lib/src/plugin/command_line_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 analyzer.src.plugin.command_line_plugin;
 
 import 'package:analyzer/plugin/command_line.dart';
 import 'package:plugin/plugin.dart';
 
 /**
@@ skipping 15 matching lines @@
 
   /**
    * The unique identifier of this plugin.
    */
   static const String UNIQUE_IDENTIFIER = 'command_line.core';
 
   /**
    * The extension point that allows plugins to register new parser
    * contributors.
    */
-  ExtensionPoint parserContributorExtensionPoint;
+  ExtensionPoint<ArgParserContributor> parserContributorExtensionPoint;
 
   /**
    * The extension point that allows plugins to register new result processors.
    */
-  ExtensionPoint resultProcessorExtensionPoint;
+  ExtensionPoint<ArgResultsProcessor> resultProcessorExtensionPoint;
 
   /**
    * Initialize a newly created plugin.
    */
   CommandLinePlugin();
 
   /**
    * Return a list containing all of the parser contributors that were
    * contributed.
    */
   List<ArgParserContributor> get parserContributors =>
       parserContributorExtensionPoint.extensions;
 
   /**
    * Return a list containing all of the result processors that were
    * contributed.
    */
   List<ArgResultsProcessor> get resultProcessors =>
       resultProcessorExtensionPoint.extensions;
 
   @override
   String get uniqueIdentifier => UNIQUE_IDENTIFIER;
 
   @override
   void registerExtensionPoints(RegisterExtensionPoint registerExtensionPoint) {
-    parserContributorExtensionPoint = registerExtensionPoint(
-        PARSER_CONTRIBUTOR_EXTENSION_POINT,
-        _validateParserContributorExtension);
-    resultProcessorExtensionPoint = registerExtensionPoint(
-        RESULT_PROCESSOR_EXTENSION_POINT, _validateResultProcessorExtension);
+    parserContributorExtensionPoint = new ExtensionPoint<ArgParserContributor>(
+        this, PARSER_CONTRIBUTOR_EXTENSION_POINT, null);
+    registerExtensionPoint(parserContributorExtensionPoint);
+    resultProcessorExtensionPoint = new ExtensionPoint<ArgResultsProcessor>(
+        this, RESULT_PROCESSOR_EXTENSION_POINT, null);
+    registerExtensionPoint(resultProcessorExtensionPoint);
   }
 
   @override
   void registerExtensions(RegisterExtension registerExtension) {
     // There are no default extensions.
   }
-
-  /**
-   * Validate the given extension by throwing an [ExtensionError] if it is not a
-   * valid parser contributor.
-   */
-  void _validateParserContributorExtension(Object extension) {
-    if (extension is! ArgParserContributor) {
-      String id = parserContributorExtensionPoint.uniqueIdentifier;
-      throw new ExtensionError(
-          'Extensions to $id must be an ArgParserContributor');
-    }
-  }
-
-  /**
-   * Validate the given extension by throwing an [ExtensionError] if it is not a
-   * valid result processor.
-   */
-  void _validateResultProcessorExtension(Object extension) {
-    if (extension is! ArgResultsProcessor) {
-      String id = resultProcessorExtensionPoint.uniqueIdentifier;
-      throw new ExtensionError(
-          'Extensions to $id must be an ArgResultsProcessor');
-    }
-  }
 }