Only mark the descriptor that is valid for the map in question. If this map

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 975fdf8d85a46b98a7d3715c09b798444efaec83..10f74fc7d6a85a264da749899f32ec02b96492e0 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2609,6 +2609,8 @@ class DescriptorArray: public FixedArray {
   inline Object** GetKeySlot(int descriptor_number);
   inline Object* GetValue(int descriptor_number);
   inline Object** GetValueSlot(int descriptor_number);
+  inline Object** GetDescriptorStartSlot(int descriptor_number);
+  inline Object** GetDescriptorEndSlot(int descriptor_number);
   inline PropertyDetails GetDetails(int descriptor_number);
   inline PropertyType GetType(int descriptor_number);
   inline int GetFieldIndex(int descriptor_number);