Update to use the new version of plugin

lib/src/plugin/linter_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 linter.src.plugin.linter_plugin;
 
 import 'package:analyzer/plugin/options.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/services/lint.dart';
 import 'package:linter/plugin/linter.dart';
@@ skipping 22 matching lines @@
   static const List<Linter> _noLints = const <Linter>[];
 
   /// The unique identifier of this plugin.
   static const String UNIQUE_IDENTIFIER = 'linter.core';
 
   /// The simple identifier of the extension point that allows plugins to
   /// register new lint rules.
   static const String LINT_RULE_EXTENSION_POINT = 'rule';
 
   /// The extension point that allows plugins to register new lint rules.
-  ExtensionPoint lintRuleExtensionPoint;
+  ExtensionPoint<LintRule> lintRuleExtensionPoint;
 
   /// An options processor for creating lint configs from analysis options.
   AnalysisOptionsProcessor _optionsProcessor;
 
   /// Cached config (temporary to support legacy `lintRules` getter).
   LintConfig _config;
 
   LinterPlugin() {
     _optionsProcessor = new AnalysisOptionsProcessor(this);
   }
 
   /// Return a list of all contributed lint rules.
   List<LintRule> get contributedRules => lintRuleExtensionPoint.extensions;
 
   /// Return a list of enabled lint rules.
   ///
   /// By default this list includes all [contributedRules].  Specific lints
   /// can be enabled/disabled (and in the future further configured) through
   /// a specified analysis options file.
   @deprecated // Use context.getConfigurationData(..)
   List<LintRule> get lintRules => _getRules(_config);
 
   @override
   String get uniqueIdentifier => UNIQUE_IDENTIFIER;
 
   @override
   void registerExtensionPoints(RegisterExtensionPoint registerExtensionPoint) {
-    lintRuleExtensionPoint = registerExtensionPoint(
-        LINT_RULE_EXTENSION_POINT, _validateTaskExtension);
+    lintRuleExtensionPoint =
+        new ExtensionPoint<LintRule>(this, LINT_RULE_EXTENSION_POINT, null);
+    registerExtensionPoint(lintRuleExtensionPoint);
   }
 
   @override
   void registerExtensions(RegisterExtension registerExtension) {
     // A subset of rules that we are considering enabled by "default".
     [
       new CamelCaseTypes(),
       new ConstantIdentifierNames(),
       new EmptyConstructorBodies(),
       new LibraryNames(),
@@ skipping 11 matching lines @@
 
   List<Linter> registerLints(AnalysisContext context, LintConfig config) {
     _config = config;
     List<Linter> lints = _getRules(config);
     setLints(context, lints);
     return lints;
   }
 
   List<Linter> _getRules(LintConfig config) =>
       config != null ? ruleRegistry.enabled(config).toList() : _noLints;
-
-  void _validateTaskExtension(Object extension) {
-    if (extension is! LintRule) {
-      String id = lintRuleExtensionPoint.uniqueIdentifier;
-      throw new ExtensionError('Extensions to $id must implement LintRule');
-    }
-  }
 }