cppgc: Fix ObjectSizeTrait

LargePage::PayloadSize inclues the heap object header.
Keeping PayloadSize as is to keep it aligned with
NormalPage::PayloadSize and introducing LargePage::ObjectSize as the
counterpart for HeapObjectHeader::ObjectSize that will exclude the
header.

Bug: chromium:1056170
Change-Id: I8a5f50841fd9dbd6c9a4a4035d9040021944cacc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2731533Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73154}

src/heap/cppgc/heap-object-header.h

@@ -73,7 +73,7 @@ class HeapObjectHeader {
   inline void SetSize(size_t size);
 
   template <AccessMode mode = AccessMode::kNonAtomic>
-  inline size_t PayloadSize() const;
+  inline size_t ObjectSize() const;
 
   template <AccessMode mode = AccessMode::kNonAtomic>
   inline bool IsLargeObject() const;
@@ -205,7 +205,7 @@ void HeapObjectHeader::SetSize(size_t size) {
 }
 
 template <AccessMode mode>
-size_t HeapObjectHeader::PayloadSize() const {
+size_t HeapObjectHeader::ObjectSize() const {
   return GetSize<mode>() - sizeof(HeapObjectHeader);
 }
 

src/heap/cppgc/heap-page.h

@@ -210,6 +210,7 @@ class V8_EXPORT_PRIVATE LargePage final : public BasePage {
   ConstAddress PayloadEnd() const;
 
   size_t PayloadSize() const { return payload_size_; }
+  size_t ObjectSize() const { return payload_size_ - sizeof(HeapObjectHeader); }
 
   bool PayloadContains(ConstAddress address) const {
     return (PayloadStart() <= address) && (address < PayloadEnd());

src/heap/cppgc/object-size-trait.cc

@@ -16,8 +16,8 @@ size_t BaseObjectSizeTrait::GetObjectSizeForGarbageCollected(
   const auto& header = HeapObjectHeader::FromPayload(object);
   return header.IsLargeObject()
              ? static_cast<const LargePage*>(BasePage::FromPayload(&header))
-                   ->PayloadSize()
-             : header.PayloadSize();
+                   ->ObjectSize()
+             : header.ObjectSize();
 }
 
 // static
@@ -29,7 +29,7 @@ size_t BaseObjectSizeTrait::GetObjectSizeForGarbageCollectedMixin(
       BasePage::FromPayload(address)
           ->ObjectHeaderFromInnerAddress<AccessMode::kAtomic>(address);
   DCHECK(!header.IsLargeObject());
-  return header.PayloadSize();
+  return header.ObjectSize();
 }
 
 }  // namespace internal