[heap] Introduce mutex for executable memory data structure

Lookups and updates to the executable_memory_ unordered_map need to be
protected with mutex.

Bug: v8:10315, v8:10546
Change-Id: Ic17e19d1e4fda18b99103a96052940e68e970586
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2208867Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67902}

src/heap/memory-allocator.h

@@ -330,12 +330,14 @@ class MemoryAllocator {
   }
 
   void RegisterExecutableMemoryChunk(MemoryChunk* chunk) {
+    base::MutexGuard guard(&executable_memory_mutex_);
     DCHECK(chunk->IsFlagSet(MemoryChunk::IS_EXECUTABLE));
     DCHECK_EQ(executable_memory_.find(chunk), executable_memory_.end());
     executable_memory_.insert(chunk);
   }
 
   void UnregisterExecutableMemoryChunk(MemoryChunk* chunk) {
+    base::MutexGuard guard(&executable_memory_mutex_);
     DCHECK_NE(executable_memory_.find(chunk), executable_memory_.end());
     executable_memory_.erase(chunk);
     chunk->heap()->UnregisterUnprotectedMemoryChunk(chunk);
@@ -396,6 +398,7 @@ class MemoryAllocator {
 
   // Data structure to remember allocated executable memory chunks.
   std::unordered_set<MemoryChunk*> executable_memory_;
+  base::Mutex executable_memory_mutex_;
 
   friend class heap::TestCodePageAllocatorScope;