Preserve constant function transition when adding the same function.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 1ca3003397c85a38593c99999c227137a5be20e5..92b24f4a105c2a4ad8131cf1d95e8b53558b871b 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1811,6 +1811,10 @@ class DescriptorArray: public FixedArray {
   // Search the instance descriptors for given name.
   inline int Search(String* name);
 
+  // As the above, but uses DescriptorLookupCache and updates it when
+  // necessary.
+  inline int SearchWithCache(String* name);
+
   // Tells whether the name is present int the array.
   bool Contains(String* name) { return kNotFound != Search(name); }