Avoid redundant calls to "pub list" when multiple dependencies change.

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';
 import 'package:analysis_server/src/services/index/index.dart';
 import 'package:analysis_server/src/services/index/local_file_index.dart';
+import 'package:analysis_server/src/source/optimizing_pub_package_map_provider.dart';
 import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
 import 'package:analyzer/plugin/plugin.dart';
-import 'package:analyzer/source/pub_package_map_provider.dart';
 import 'package:analyzer/src/generated/sdk_io.dart';
 
 /**
  * Instances of the class [SocketServer] implement the common parts of
  * http-based and stdio-based analysis servers.  The primary responsibility of
  * the SocketServer is to manage the lifetime of the AnalysisServer and to
  * encode and decode the JSON messages exchanged with the client.
  */
 class SocketServer {
   final AnalysisServerOptions analysisServerOptions;
@@ skipping 41 matching lines @@
           'File read mode was set to the unknown mode: $analysisServerOptions.fileReadMode');
     }
 
     Index index = null;
     if (!analysisServerOptions.noIndex) {
       index = createLocalFileIndex();
       index.run();
     }
 
     analysisServer = new AnalysisServer(serverChannel, resourceProvider,
-        new PubPackageMapProvider(resourceProvider, defaultSdk), index,
+        new OptimizingPubPackageMapProvider(resourceProvider, defaultSdk), index,
         analysisServerOptions, defaultSdk, instrumentationService,
         rethrowExceptions: false);
     _initializeHandlers(analysisServer);
     analysisServer.userDefinedPlugins = userDefinedPlugins;
   }
 
   /**
    * Initialize the handlers to be used by the given [server].
    */
   void _initializeHandlers(AnalysisServer server) {
     server.handlers = serverPlugin.createDomains(server);
   }
 }