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

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 28d8762e9e0192ccc6c368e5b9709071ad39fced..18894c1d56123f99fe02df5967ea06ffdac8a857 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -2142,6 +2142,16 @@ Object** DescriptorArray::GetKeySlot(int descriptor_number) {
 }
 
 
+Object** DescriptorArray::GetDescriptorStartSlot(int descriptor_number) {
+  return GetKeySlot(descriptor_number);
+}
+
+
+Object** DescriptorArray::GetDescriptorEndSlot(int descriptor_number) {
+  return GetValueSlot(descriptor_number - 1) + 1;
+}
+
+
 String* DescriptorArray::GetKey(int descriptor_number) {
   ASSERT(descriptor_number < number_of_descriptors());
   return String::cast(get(ToKeyIndex(descriptor_number)));