Don't use "final" in analysis server protocol classes.

pkg/analysis_server/tool/spec/codegen_dart_protocol.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 codegen.protocol;
 
 import 'dart:convert';
 
 import 'api.dart';
 import 'codegen_tools.dart';
@@ skipping 221 matching lines @@
     }));
     writeln('class $className implements HasToJson {');
     indent(() {
       for (TypeObjectField field in type.fields) {
         if (field.value != null) {
           continue;
         }
         docComment(toHtmlVisitor.collectHtml(() {
           toHtmlVisitor.translateHtml(field.html);
         }));
-        writeln('final ${dartType(field.type)} ${field.name};');
+        writeln('${dartType(field.type)} ${field.name};');
         writeln();
       }
       emitObjectConstructor(type, className);
       writeln();
       emitObjectFromJsonConstructor(className, type, impliedType);
       writeln();
       if (emitConvenienceConstructor(className, impliedType)) {
         writeln();
       }
       emitToJsonMember(type);
@@ skipping 575 matching lines @@
   CodegenProtocolVisitor visitor = new CodegenProtocolVisitor(readApi());
   return visitor.collectCode(visitor.visitApi);
 });
 
 /**
  * Translate spec_input.html into protocol_matchers.dart.
  */
 main() {
   target.generate();
 }