Reapply descriptor array sharing.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index fc5fb36142797cfbd2cc4658f84d679efa10b41c..bdb63bffc0f15e8fdcaed1cae9f0e03f6cb63fee 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -2052,7 +2052,9 @@ MaybeObject* Heap::AllocatePartialMap(InstanceType instance_type,
   reinterpret_cast<Map*>(result)->set_unused_property_fields(0);
   reinterpret_cast<Map*>(result)->set_bit_field(0);
   reinterpret_cast<Map*>(result)->set_bit_field2(0);
-  reinterpret_cast<Map*>(result)->set_bit_field3(0);
+  int bit_field3 = Map::EnumLengthBits::encode(Map::kInvalidEnumCache) |
+                   Map::OwnsDescriptors::encode(true);
+  reinterpret_cast<Map*>(result)->set_bit_field3(bit_field3);
   return result;
 }
 
@@ -2079,7 +2081,8 @@ MaybeObject* Heap::AllocateMap(InstanceType instance_type,
   map->set_unused_property_fields(0);
   map->set_bit_field(0);
   map->set_bit_field2(1 << Map::kIsExtensible);
-  int bit_field3 = Map::EnumLengthBits::encode(Map::kInvalidEnumCache);
+  int bit_field3 = Map::EnumLengthBits::encode(Map::kInvalidEnumCache) |
+                   Map::OwnsDescriptors::encode(true);
   map->set_bit_field3(bit_field3);
   map->set_elements_kind(elements_kind);
 
@@ -7123,7 +7126,7 @@ void KeyedLookupCache::Clear() {
 
 
 void DescriptorLookupCache::Clear() {
-  for (int index = 0; index < kLength; index++) keys_[index].array = NULL;
+  for (int index = 0; index < kLength; index++) keys_[index].source = NULL;
 }