[handles] Check FLAG_local_heaps in IsDereferenceAllowed()

While LocalHeap allow to dereference handles on background threads, this
is only possible when FLAG_local_heaps is enabled.

Bug: v8:10315
Change-Id: Ia27582cda7e4b4faf4d2c76959de418415e1ae68
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2372147
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69557}

src/handles/handles.cc

@@ -43,7 +43,7 @@ bool HandleBase::IsDereferenceAllowed() const {
   }
 
   LocalHeap* local_heap = LocalHeap::Current();
-  if (V8_UNLIKELY(local_heap)) {
+  if (FLAG_local_heaps && local_heap) {
     // Local heap can't access handles when parked
     if (!local_heap->IsHandleDereferenceAllowed()) return false;
 

test/cctest/compiler/serializer-tester.cc

@@ -31,6 +31,7 @@ SerializerTester::SerializerTester(const char* source)
   // We need allocation of executable memory for the compilation.
   FLAG_jitless = false;
   FLAG_allow_natives_syntax = true;
+  FlagList::EnforceFlagImplications();
 
   std::string function_string = "(function() { ";
   function_string += source;