Reland "Only use FreeSpace objects in the free list"

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 5ee91913251c81f4833f9230afc419b59f7db384..402010e91a7d8058eb9d45971cdcc2e27f60dbb3 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -3334,7 +3334,6 @@ CAST_ACCESSOR(FixedArrayBase)
 CAST_ACCESSOR(FixedDoubleArray)
 CAST_ACCESSOR(FixedTypedArrayBase)
 CAST_ACCESSOR(Foreign)
-CAST_ACCESSOR(FreeSpace)
 CAST_ACCESSOR(GlobalObject)
 CAST_ACCESSOR(HeapObject)
 CAST_ACCESSOR(JSArray)
@@ -3443,6 +3442,39 @@ SMI_ACCESSORS(String, length, kLengthOffset)
 SYNCHRONIZED_SMI_ACCESSORS(String, length, kLengthOffset)
 
 
+FreeSpace* FreeSpace::next() {
+  DCHECK(map() == GetHeap()->raw_unchecked_free_space_map() ||
+         (!GetHeap()->deserialization_complete() && map() == NULL));
+  DCHECK_LE(kNextOffset + kPointerSize, nobarrier_size());
+  return reinterpret_cast<FreeSpace*>(
+      Memory::Address_at(address() + kNextOffset));
+}
+
+
+FreeSpace** FreeSpace::next_address() {
+  DCHECK(map() == GetHeap()->raw_unchecked_free_space_map() ||
+         (!GetHeap()->deserialization_complete() && map() == NULL));
+  DCHECK_LE(kNextOffset + kPointerSize, nobarrier_size());
+  return reinterpret_cast<FreeSpace**>(address() + kNextOffset);
+}
+
+
+void FreeSpace::set_next(FreeSpace* next) {
+  DCHECK(map() == GetHeap()->raw_unchecked_free_space_map() ||
+         (!GetHeap()->deserialization_complete() && map() == NULL));
+  DCHECK_LE(kNextOffset + kPointerSize, nobarrier_size());
+  base::NoBarrier_Store(
+      reinterpret_cast<base::AtomicWord*>(address() + kNextOffset),
+      reinterpret_cast<base::AtomicWord>(next));
+}
+
+
+FreeSpace* FreeSpace::cast(HeapObject* o) {
+  SLOW_DCHECK(!o->GetHeap()->deserialization_complete() || o->IsFreeSpace());
+  return reinterpret_cast<FreeSpace*>(o);
+}
+
+
 uint32_t Name::hash_field() {
   return READ_UINT32_FIELD(this, kHashFieldOffset);
 }