Properly initialize Isolate::last_long_task_stats_counter_

Bug: chromium:1173527
Change-Id: Ib5ec5732b442539ad112acaef3c2898f03082650
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2835733Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74188}

src/execution/isolate.h

@@ -2069,7 +2069,7 @@ class V8_EXPORT_PRIVATE Isolate final : private HiddenFactory {
       Persistent<v8::Context, v8::CopyablePersistentTraits<v8::Context>>>
       recorder_context_id_map_;
 
-  size_t last_long_task_stats_counter_;
+  size_t last_long_task_stats_counter_ = 0;
   v8::metrics::LongTaskStats long_task_stats_;
 
   std::vector<Object> startup_object_cache_;