Internalize strings being stored into uninitialized property cells

src/lookup.h

Index: src/lookup.h
diff --git a/src/lookup.h b/src/lookup.h
index a78bb5d91d658cd7d1e04c709d5c0fe9f731cf61..b197b76971cfe302cebe0898d1eb980b9b1791a9 100644
--- a/src/lookup.h
+++ b/src/lookup.h
@@ -136,7 +136,9 @@ class LookupIterator FINAL BASE_EMBEDDED {
   Handle<PropertyCell> GetPropertyCell() const;
   Handle<Object> GetAccessors() const;
   Handle<Object> GetDataValue() const;
-  void WriteDataValue(Handle<Object> value);
+  // Usually returns the value that was passed in, but may perform
+  // non-observable modifications on it, such as internalize strings.
+  Handle<Object> WriteDataValue(Handle<Object> value);
 
   // Checks whether the receiver is an indexed exotic object
   // and name is a special numeric index.