Implement tracking and optimizations of packed arrays

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index beb1bc511e6fceb5c3d09dbc5805a8c409da2b97..55e7135609b94db45e63834f852a18a2dcc8b683 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -621,7 +621,7 @@ class Heap {
   MUST_USE_RESULT MaybeObject* AllocateMap(
       InstanceType instance_type,
       int instance_size,
-      ElementsKind elements_kind = FAST_ELEMENTS);
+      ElementsKind elements_kind = TERMINAL_FAST_ELEMENTS_KIND);
 
   // Allocates a partial map for bootstrapping.
   MUST_USE_RESULT MaybeObject* AllocatePartialMap(InstanceType instance_type,