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

pkg/analysis_server/tool/spec/codegen_dart_protocol.dart

Index: pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
diff --git a/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart b/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
index 471a1487e1f93a08b1b4445f505b239375de58f2..96c158cffdb2059160065eebba7baf74c504cf01 100644
--- a/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
+++ b/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
@@ -239,7 +239,7 @@ class CodegenProtocolVisitor extends HierarchicalApiVisitor with CodeGenerator {
         docComment(toHtmlVisitor.collectHtml(() {
           toHtmlVisitor.translateHtml(field.html);
         }));
-        writeln('final ${dartType(field.type)} ${field.name};');
+        writeln('${dartType(field.type)} ${field.name};');
         writeln();
       }
       emitObjectConstructor(type, className);