Meaningful name for builtins in JitCodeEvent API.

Report builtins by name (e.g. "Builtin:ArgumentsAdaptorTrampoline")
instead of labeling everything "Builtin:A builtin from the snapshot".

BUG=

Review URL: https://codereview.chromium.org/1216833002

Cr-Commit-Position: refs/heads/master@{#29339}

src/log.cc

@@ -1610,7 +1610,7 @@ void Logger::LogCodeObject(Object* object) {
       tag = Logger::REG_EXP_TAG;
       break;
     case Code::BUILTIN:
-      description = "A builtin from the snapshot";
+      description = isolate_->builtins()->name(code_object->builtin_index());
       tag = Logger::BUILTIN_TAG;
       break;
     case Code::HANDLER: