Increment descriptor array slack for prototypes by a constant rather than 50%

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 0007b37ca99a85ebc7643c9309e7a78834847e5d..0e43e1d3a0fbd434bf311fa3dffc579b3b73a3ee 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -5092,6 +5092,7 @@ ACCESSORS(CallHandlerInfo, callback, Object, kCallbackOffset)
 ACCESSORS(CallHandlerInfo, data, Object, kDataOffset)
 
 ACCESSORS(TemplateInfo, tag, Object, kTagOffset)
+SMI_ACCESSORS(TemplateInfo, number_of_properties, kNumberOfProperties)
 ACCESSORS(TemplateInfo, property_list, Object, kPropertyListOffset)
 ACCESSORS(TemplateInfo, property_accessors, Object, kPropertyAccessorsOffset)
 
@@ -6945,11 +6946,13 @@ void Map::ClearCodeCache(Heap* heap) {
 }
 
 
-int Map::SlackForArraySize(int old_size, int size_limit) {
+int Map::SlackForArraySize(bool is_prototype_map, int old_size,
+                           int size_limit) {
   const int max_slack = size_limit - old_size;
-  CHECK(max_slack >= 0);
+  CHECK_LE(0, max_slack);
   if (old_size < 4) return Min(max_slack, 1);
-  return Min(max_slack, old_size / 2);
+  if (is_prototype_map) return Min(max_slack, 4);
+  return Min(max_slack, old_size / 4);
 }