Move the wire protocol support into the public API

pkg/analysis_server/test/analysis/notification_occurrences_test.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 test.analysis.notification.occurrences;
 
 import 'dart:async';
 
+import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/constants.dart';
-import 'package:analysis_server/src/protocol.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 import 'package:unittest/unittest.dart';
 
 import '../analysis_abstract.dart';
 import '../utils.dart';
 
 main() {
   initializeTestEnvironment();
   defineReflectiveTests(AnalysisNotificationOccurrencesTest);
 }
@@ skipping 234 matching lines @@
     addTestFile('''
 void main() {
 }
 ''');
     return prepareOccurrences().then((_) {
       int offset = findOffset('void main()');
       findRegion(offset, 'void'.length, false);
     });
   }
 }