After transitioning to constant function, return the constant function as result of the assignment.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 986198808569a3c52f86d87f741aab1600509707..cd2eebf0bcaa160cc0de20d4f794f858d928f5e7 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -2959,7 +2959,7 @@ MaybeObject* JSObject::SetPropertyForResult(LookupResult* result,
       // transition to the target map.
       if (constant_function == *value) {
         self->set_map(transition_map);
-        return this;
+        return constant_function;
       }
       // Otherwise, replace with a map transition to a new map with a FIELD,
       // even if the value is a constant function.