fix #27258, don't allow dynamic set of a final field

pkg/dev_compiler/test/codegen_expected/BenchmarkBase.js

Index: pkg/dev_compiler/test/codegen_expected/BenchmarkBase.js
diff --git a/pkg/dev_compiler/test/codegen_expected/BenchmarkBase.js b/pkg/dev_compiler/test/codegen_expected/BenchmarkBase.js
index 20b9dceb62a5e7d88921d63f39def68d8957cef8..cca6c6a3ad3a20151a307d72732a8a6ec60606b3 100644
--- a/pkg/dev_compiler/test/codegen_expected/BenchmarkBase.js
+++ b/pkg/dev_compiler/test/codegen_expected/BenchmarkBase.js
@@ -83,7 +83,7 @@ define(['dart_sdk'], function(dart_sdk) {
   };
   const name$ = Symbol("BenchmarkBase.name");
   dart.setSignature(BenchmarkBase$.BenchmarkBase, {
-    fields: () => ({name: core.String}),
+    fields: () => ({name: dart.finalFieldType(core.String)}),
     methods: () => ({
       run: dart.definiteFunctionType(dart.void, []),
       warmup: dart.definiteFunctionType(dart.void, []),