Tenure long-living descriptor arrays.

BUG=chromium:580971
LOG=n

Review URL: https://codereview.chromium.org/1681533003

Cr-Commit-Position: refs/heads/master@{#33840}

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));

src/objects.h

@@ -2983,9 +2983,9 @@ class DescriptorArray: public FixedArray {
 
   // Allocates a DescriptorArray, but returns the singleton
   // empty descriptor array object if number_of_descriptors is 0.
-  static Handle<DescriptorArray> Allocate(Isolate* isolate,
-                                          int number_of_descriptors,
-                                          int slack = 0);
+  static Handle<DescriptorArray> Allocate(
+      Isolate* isolate, int number_of_descriptors, int slack,
+      PretenureFlag pretenure = NOT_TENURED);
 
   DECLARE_CAST(DescriptorArray)