Move the wire protocol support into the public API

pkg/analysis_server/lib/src/plugin/server_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.plugin.server_plugin;
 
 import 'package:analysis_server/plugin/analysis/analysis_domain.dart';
 import 'package:analysis_server/plugin/analysis/analyzed_files.dart';
 import 'package:analysis_server/plugin/analysis/navigation/navigation.dart';
 import 'package:analysis_server/plugin/analysis/navigation/navigation_core.dart';
 import 'package:analysis_server/plugin/analysis/occurrences/occurrences.dart';
 import 'package:analysis_server/plugin/analysis/occurrences/occurrences_core.dart';
 import 'package:analysis_server/plugin/edit/assist/assist.dart';
 import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/plugin/edit/fix/fix.dart';
 import 'package:analysis_server/plugin/edit/fix/fix_core.dart';
 import 'package:analysis_server/plugin/index/index.dart';
 import 'package:analysis_server/plugin/index/index_core.dart';
+import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/domain_analysis.dart';
 import 'package:analysis_server/src/domain_completion.dart';
 import 'package:analysis_server/src/domain_execution.dart';
 import 'package:analysis_server/src/domain_server.dart';
 import 'package:analysis_server/src/domains/analysis/navigation_dart.dart';
 import 'package:analysis_server/src/domains/analysis/occurrences_dart.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
-import 'package:analysis_server/src/protocol.dart';
 import 'package:analysis_server/src/provisional/completion/completion_core.dart';
 import 'package:analysis_server/src/search/search_domain.dart';
 import 'package:analysis_server/src/services/correction/assist_internal.dart';
 import 'package:analysis_server/src/services/correction/fix_internal.dart';
 import 'package:analysis_server/src/services/index/index_contributor.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:plugin/plugin.dart';
 
 /**
@@ skipping 377 matching lines @@
    * valid analysis domain receiver.
    */
   void _validateSetAnalysisDomainFunction(Object extension) {
     if (extension is! SetAnalysisDomain) {
       String id = setAnalysisDomainExtensionPoint.uniqueIdentifier;
       throw new ExtensionError(
           'Extensions to $id must be a SetAnalysisDomain function');
     }
   }
 }