Tenure long-living descriptor arrays.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index e6fc951513ce89e4fc91cfbfa1c400309c67a52b..c522035e39f9a4caaa4379b9e2602bf4fd750028 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -5710,7 +5710,7 @@ void JSObject::MigrateSlowToFast(Handle<JSObject> object,
 
   // Allocate the instance descriptor.
   Handle<DescriptorArray> descriptors = DescriptorArray::Allocate(
-      isolate, instance_descriptor_length);
+      isolate, instance_descriptor_length, 0, TENURED);
 
   int number_of_allocated_fields =
       number_of_fields + unused_property_fields - inobject_props;
@@ -10914,17 +10914,18 @@ Handle<ArrayList> ArrayList::EnsureSpace(Handle<ArrayList> array, int length) {
   return array;
 }
 
-
 Handle<DescriptorArray> DescriptorArray::Allocate(Isolate* isolate,
                                                   int number_of_descriptors,
-                                                  int slack) {
+                                                  int slack,
+                                                  PretenureFlag pretenure) {
   DCHECK(0 <= number_of_descriptors);
   Factory* factory = isolate->factory();
   // Do not use DescriptorArray::cast on incomplete object.
   int size = number_of_descriptors + slack;
   if (size == 0) return factory->empty_descriptor_array();
   // Allocate the array of keys.
-  Handle<FixedArray> result = factory->NewFixedArray(LengthFor(size));
+  Handle<FixedArray> result =
+      factory->NewFixedArray(LengthFor(size), pretenure);
 
   result->set(kDescriptorLengthIndex, Smi::FromInt(number_of_descriptors));
   result->set(kEnumCacheIndex, Smi::FromInt(0));