[V8] Reset IsolateData only after disposing the Isolate

Calling Isolate::Dispose before resetting the isolate_data
makes sure all threads which might access PerIsolateData are finished.

Bug: chromium:1278990
Change-Id: Icdf62f583b574bc83b7dacd3444ea618f395f9fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3341061
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#955784}

gin/isolate_holder.cc

@@ -106,8 +106,10 @@ IsolateHolder::IsolateHolder(
 
 IsolateHolder::~IsolateHolder() {
   isolate_memory_dump_provider_.reset();
-  isolate_data_.reset();
+  // Calling Isolate::Dispose makes sure all threads which might access
+  // PerIsolateData are finished.
   isolate_->Dispose();
+  isolate_data_.reset();
   isolate_ = nullptr;
 }
 

gin/per_isolate_data.cc

@@ -42,9 +42,7 @@ PerIsolateData::PerIsolateData(
   }
 }
 
-PerIsolateData::~PerIsolateData() {
-  isolate_->SetData(kEmbedderNativeGin, NULL);
-}
+PerIsolateData::~PerIsolateData() = default;
 
 PerIsolateData* PerIsolateData::From(Isolate* isolate) {
   return static_cast<PerIsolateData*>(isolate->GetData(kEmbedderNativeGin));