Preallocate space in descriptor arrays.

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 462af590d2f02ab592062ffe5f943e2cf31fc812..a2bb9391ee64fb2bf8fe7332c39353d8fef19999 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -112,10 +112,11 @@ Handle<ObjectHashTable> Factory::NewObjectHashTable(int at_least_space_for) {
 }
 
 
-Handle<DescriptorArray> Factory::NewDescriptorArray(int number_of_descriptors) {
+Handle<DescriptorArray> Factory::NewDescriptorArray(int number_of_descriptors,
+                                                    int slack) {
   ASSERT(0 <= number_of_descriptors);
   CALL_HEAP_FUNCTION(isolate(),
-                     DescriptorArray::Allocate(number_of_descriptors),
+                     DescriptorArray::Allocate(number_of_descriptors, slack),
                      DescriptorArray);
 }
 
@@ -1284,10 +1285,26 @@ Handle<JSFunction> Factory::CreateApiFunction(
   result->shared()->DontAdaptArguments();
 
   // Recursively copy parent templates' accessors, 'data' may be modified.
+  int max_number_of_additional_properties = 0;
+  FunctionTemplateInfo* info = *obj;
+  while (true) {
+    Object* props = info->property_accessors();
+    if (!props->IsUndefined()) {
+      Handle<Object> props_handle(props);
+      NeanderArray props_array(props_handle);
+      max_number_of_additional_properties += props_array.length();
+    }
+    Object* parent = info->parent_template();
+    if (parent->IsUndefined()) break;
+    info = FunctionTemplateInfo::cast(parent);
+  }
+
+  Map::EnsureDescriptorSlack(map, max_number_of_additional_properties);
+
   while (true) {
     Handle<Object> props = Handle<Object>(obj->property_accessors());
     if (!props->IsUndefined()) {
-      Map::CopyAppendCallbackDescriptors(map, props);
+      Map::AppendCallbackDescriptors(map, props);
     }
     Handle<Object> parent = Handle<Object>(obj->parent_template());
     if (parent->IsUndefined()) break;