[heap] Color object black on unsafe layout change.

src/heap/incremental-marking.h

Index: src/heap/incremental-marking.h
diff --git a/src/heap/incremental-marking.h b/src/heap/incremental-marking.h
index 8f86dcb703f4d4582d9c648d8986a2131c5526af..998d0b279e9639cb72146aa45d85131dffaff1eb 100644
--- a/src/heap/incremental-marking.h
+++ b/src/heap/incremental-marking.h
@@ -223,6 +223,11 @@ class V8_EXPORT_PRIVATE IncrementalMarking {
   // from white to grey.
   bool WhiteToGreyAndPush(HeapObject* obj);
 
+  // This function is used to color the object black before it undergoes an
+  // unsafe layout change. This is a part of synchronization protocol with
+  // the concurrent marker.
+  void MarkBlackAndPush(HeapObject* obj);
+
   inline void SetOldSpacePageFlags(MemoryChunk* chunk) {
     SetOldSpacePageFlags(chunk, IsMarking(), IsCompacting());
   }