Refactor Map::ConstructionCount.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 6502de3a9b43ff96f9c0cda1f9d7217222246331..416bcc82862bf4dcb403cc75a5afcf3daa2d4c32 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -2365,7 +2365,8 @@ AllocationResult Heap::AllocatePartialMap(InstanceType instance_type,
   reinterpret_cast<Map*>(result)->set_bit_field(0);
   reinterpret_cast<Map*>(result)->set_bit_field2(0);
   int bit_field3 = Map::EnumLengthBits::encode(kInvalidEnumCacheSentinel) |
-                   Map::OwnsDescriptors::encode(true);
+                   Map::OwnsDescriptors::encode(true) |
+                   Map::Counter::encode(Map::kRetainingCounterStart);
   reinterpret_cast<Map*>(result)->set_bit_field3(bit_field3);
   return result;
 }
@@ -2401,7 +2402,8 @@ AllocationResult Heap::AllocateMap(InstanceType instance_type,
   map->set_bit_field(0);
   map->set_bit_field2(1 << Map::kIsExtensible);
   int bit_field3 = Map::EnumLengthBits::encode(kInvalidEnumCacheSentinel) |
-                   Map::OwnsDescriptors::encode(true);
+                   Map::OwnsDescriptors::encode(true) |
+                   Map::Counter::encode(Map::kRetainingCounterStart);
   map->set_bit_field3(bit_field3);
   map->set_elements_kind(elements_kind);