Move index closer to the plugin API

pkg/analysis_server/lib/src/socket_server.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 socket.server;
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/channel/channel.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:analysis_server/src/protocol.dart';
@@ skipping 53 matching lines @@
       resourceProvider = new PhysicalResourceProvider(
           PhysicalResourceProvider.NORMALIZE_EOL_ALWAYS);
     } else {
       throw new Exception(
           'File read mode was set to the unknown mode: $analysisServerOptions.fileReadMode');
     }
 
     Index index = null;
     if (!analysisServerOptions.noIndex) {
       index = createLocalFileIndex();
+      index.contributors = serverPlugin.indexContributors;
       index.run();
     }
 
     analysisServer = new AnalysisServer(serverChannel, resourceProvider,
         new OptimizingPubPackageMapProvider(resourceProvider, defaultSdk),
         index, serverPlugin, analysisServerOptions, defaultSdk,
         instrumentationService, rethrowExceptions: false);
     analysisServer.userDefinedPlugins = userDefinedPlugins;
   }
 }