Move the wire protocol support into the public API

pkg/analysis_server/test/domain_execution_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.domain.execution;
 
 import 'dart:async';
 
+import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
 import 'package:analysis_server/src/context_manager.dart';
 import 'package:analysis_server/src/domain_execution.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
-import 'package:analysis_server/src/protocol.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/source_io.dart';
 import 'package:plugin/manager.dart';
 import 'package:typed_mock/typed_mock.dart';
 import 'package:unittest/unittest.dart';
 
@@ skipping 298 matching lines @@
  * A [Source] that knows it's [fullName].
  */
 class TestSource implements Source {
   String fullName;
 
   TestSource(this.fullName);
 
   @override
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }