[heap] Annotate write barrier branches with likely/unlikely

Change-Id: Idc2a9019f5b0e67860edd8620a6cb0ed7002b1df
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3910029Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83369}

src/heap/heap-write-barrier-inl.h

@@ -115,7 +115,7 @@ inline void CombinedWriteBarrierInternal(HeapObject host, HeapObjectSlot slot,
   }
 
   // Marking barrier: mark value & record slots when marking is on.
-  if (is_marking) {
+  if (V8_UNLIKELY(is_marking)) {
 #ifdef V8_EXTERNAL_CODE_SPACE
     // CodePageHeaderModificationScope is not required because the only case
     // when a Code value is stored somewhere is during creation of a new Code
@@ -259,7 +259,7 @@ base::Optional<Heap*> WriteBarrier::GetHeapIfMarking(HeapObject object) {
   if (V8_ENABLE_THIRD_PARTY_HEAP_BOOL) return {};
   heap_internals::MemoryChunk* chunk =
       heap_internals::MemoryChunk::FromHeapObject(object);
-  if (!chunk->IsMarking()) return {};
+  if (V8_LIKELY(!chunk->IsMarking())) return {};
   return chunk->GetHeap();
 }