Internalize strings being stored into uninitialized property cells

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 02b8a0b34549a4ea04a9f7d0f25d4901a4ee3790..92d134f518e82233440d799ced586131ab1f4bf4 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -9658,8 +9658,10 @@ class PropertyCell: public Cell {
   // of the cell's current type and the value's type. If the change causes
   // a change of the type of the cell's contents, code dependent on the cell
   // will be deoptimized.
-  static void SetValueInferType(Handle<PropertyCell> cell,
-                                Handle<Object> value);
+  // Usually returns the value that was passed in, but may perform
+  // non-observable modifications on it, such as internalize strings.
+  static Handle<Object> SetValueInferType(Handle<PropertyCell> cell,
+                                          Handle<Object> value);
 
   // Computes the new type of the cell's contents for the given value, but
   // without actually modifying the 'type' field.