[heap] Fix data race in large code space

Data race access to chunk_map_. The main thread can read the map
while the background thread (concurrent SP compiler) adds a new page
to the map.

Bug: v8:12054
Change-Id: Ie7c596f3d3aeb4dca9cc6f41ed16f39dcafc7871
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3256547
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Auto-Submit: Victor Gomes <victorgomes@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77654}

src/heap/large-spaces.cc

@@ -216,6 +216,7 @@ size_t LargeObjectSpace::CommittedPhysicalMemory() {
 }
 
 LargePage* CodeLargeObjectSpace::FindPage(Address a) {
+  base::MutexGuard guard(&allocation_mutex_);
   const Address key = BasicMemoryChunk::FromAddress(a)->address();
   auto it = chunk_map_.find(key);
   if (it != chunk_map_.end()) {