[heap] Notify GC on potentially unsafe object layout changes.

src/objects-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 1450 matching lines @@
       map_word().ToRawValue() & ~static_cast<uintptr_t>(PathTracer::kMarkTag);
   return MapWord::FromRawValue(raw_value).ToMap();
 #else
   return map_word().ToMap();
 #endif
 }
 
 
 void HeapObject::set_map(Map* value) {
   set_map_word(MapWord::FromMap(value));
-  if (value != NULL) {
+  if (value != nullptr) {
     // TODO(1600) We are passing NULL as a slot because maps can never be on
     // evacuation candidate.
-    value->GetHeap()->incremental_marking()->RecordWrite(this, NULL, value);
+    value->GetHeap()->incremental_marking()->RecordWrite(this, nullptr, value);
+#ifdef VERIFY_HEAP
+    value->GetHeap()->VerifyObjectLayoutChange(this, value);
+#endif
   }
 }
 
 
 Map* HeapObject::synchronized_map() {
   return synchronized_map_word().ToMap();
 }
 
 
 void HeapObject::synchronized_set_map(Map* value) {
   synchronized_set_map_word(MapWord::FromMap(value));
-  if (value != NULL) {
+  if (value != nullptr) {
     // TODO(1600) We are passing NULL as a slot because maps can never be on
     // evacuation candidate.
-    value->GetHeap()->incremental_marking()->RecordWrite(this, NULL, value);
+    value->GetHeap()->incremental_marking()->RecordWrite(this, nullptr, value);
+#ifdef VERIFY_HEAP
+    value->GetHeap()->VerifyObjectLayoutChange(this, value);
+#endif
   }
 }
 
 
 void HeapObject::synchronized_set_map_no_write_barrier(Map* value) {
   synchronized_set_map_word(MapWord::FromMap(value));
 }
 
 
 // Unsafe accessor omitting write barrier.
@@ skipping 6749 matching lines @@
 #undef WRITE_INT64_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_OBJECTS_INL_H_