[ptr-compr] Use RelaxedLoad() in FullObjectSlot::contains_value()

to make TSAN happy.

Bug: v8:8518
Change-Id: I1c7291cc6035c7e88758d867cb74467c59e95ef1
No-Tree-Checks: true
Reviewed-on: https://chromium-review.googlesource.com/c/1365285Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58075}

src/objects/slots-inl.h

@@ -24,7 +24,7 @@ FullObjectSlot::FullObjectSlot(ObjectPtr* object)
     : SlotBase(reinterpret_cast<Address>(&object->ptr_)) {}
 
 bool FullObjectSlot::contains_value(Address raw_value) const {
-  return *location() == raw_value;
+  return base::AsAtomicPointer::Relaxed_Load(location()) == raw_value;
 }
 
 Object* FullObjectSlot::operator*() const {