Generate constants in server as we do in plugin

pkg/analysis_server/tool/spec/codegen_protocol_constants.dart

 // Copyright (c) 2017, 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.
 
 import 'package:analyzer/src/codegen/tools.dart';
 import 'package:front_end/src/codegen/tools.dart';
 
 import 'api.dart';
 import 'codegen_dart.dart';
 import 'from_html.dart';
@@ skipping 106 matching lines @@
    * Generate a constant for each of the fields in the given [type], where the
    * name of each constant will be composed from the [parentName] and the name
    * of the field.
    */
   void _addFieldConstants(String parentName, TypeObject type) {
     if (type == null) {
       return;
     }
     type.fields.forEach((TypeObjectField field) {
       String name = field.name;
-      String fieldConstantName = parentName + '_' + name.toUpperCase();
+      List<String> components = <String>[];
+      components.add(parentName);
+      components.addAll(_split(name));
+      String fieldConstantName = _fromComponents(components);
       constants.add(new _Constant(fieldConstantName, "'$name'"));
     });
   }
 
   /**
+   * Return a name generated by converting each of the given [components] to an
+   * uppercase equivalent, then joining them with underscores.
+   */
+  String _fromComponents(List<String> components) =>
+      components.map((String component) => component.toUpperCase()).join('_');
+
+  /**
    * Generate a name from the [domainName], [kind] and [name] components.
    */
   String _generateName(String domainName, String kind, String name) {
     List<String> components = <String>[];
     components.addAll(_split(domainName));
     components.add(kind);
     components.addAll(_split(name));
-    return components
-        .map((String component) => component.toUpperCase())
-        .join('_');
+    return _fromComponents(components);
   }
 
   /**
    * Return the components of the given [string] that are indicated by an upper
    * case letter.
    */
   Iterable<String> _split(String first) {
     RegExp regExp = new RegExp('[A-Z]');
     List<String> components = <String>[];
     int start = 1;
     int index = first.indexOf(regExp, start);
     while (index >= 0) {
       components.add(first.substring(start - 1, index));
       start = index + 1;
       index = first.indexOf(regExp, start);
     }
     components.add(first.substring(start - 1));
     return components;
   }
 }