[heap] LocalHeap::IsParked doesn't need mutex

We only use IsParked from the thread that owns the LocalHeap, which is
the only thread which mutates state_. So it is safe to read state_ from
that thread without a mutex.

Bug: v8:10315
Change-Id: I3725ca4c4c4da1c661d7b4f06d295312914b4b52
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2332168Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69172}

src/heap/local-heap.cc

@@ -81,7 +81,7 @@ bool LocalHeap::IsHandleDereferenceAllowed() {
 #endif
 
 bool LocalHeap::IsParked() {
-  base::MutexGuard guard(&state_mutex_);
+  DCHECK_EQ(LocalHeap::Current(), this);
   return state_ == ThreadState::Parked;
 }