Move the wire protocol support into the public API

pkg/analysis_server/test/src/utilities/change_builder_dart_test.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.test.src.utilities.change_builder_dart_test;
 
 import 'package:analysis_server/plugin/edit/utilities/change_builder_dart.dart';
-import 'package:analysis_server/src/protocol.dart';
+import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/utilities/change_builder_dart.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../abstract_context.dart';
 import '../../utils.dart';
 
 main() {
@@ skipping 751 matching lines @@
       DartEditBuilderImpl editBuilder =
           builder.createEditBuilder(offset, length);
       expect(editBuilder, new isInstanceOf<DartEditBuilder>());
       SourceEdit sourceEdit = editBuilder.sourceEdit;
       expect(sourceEdit.length, length);
       expect(sourceEdit.offset, offset);
       expect(sourceEdit.replacement, isEmpty);
     });
   }
 }