Reland "Only use FreeSpace objects in the free list"

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 2ae4165b9965cf4892cbf92be5daf1bf2dfdc271..4ccbd040b4fe23c3e9a3eba1e5902292c5d604f1 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -692,8 +692,8 @@ class Heap {
   // Iterates the whole code space to clear all ICs of the given kind.
   void ClearAllICsByKind(Code::Kind kind);
 
-  // For use during bootup.
-  void RepairFreeListsAfterBoot();
+  // FreeSpace objects have a null map after deserialization. Update the map.
+  void RepairFreeListsAfterDeserialization();
 
   template <typename T>
   static inline bool IsOneByte(T t, int chars);