Use mutable heapnumbers to store doubles in fields.

src/objects-printer.cc

Index: src/objects-printer.cc
diff --git a/src/objects-printer.cc b/src/objects-printer.cc
index 5aeeec6567ece92a4613ce1a9366b3b35085ec67..0849a630c230205b8f299e74dd85de4eb2c5845a 100644
--- a/src/objects-printer.cc
+++ b/src/objects-printer.cc
@@ -271,7 +271,7 @@ void JSObject::PrintProperties(FILE* out) {
       switch (descs->GetType(i)) {
         case FIELD: {
           int index = descs->GetFieldIndex(i);
-          FastPropertyAt(index)->ShortPrint(out);
+          RawFastPropertyAt(index)->ShortPrint(out);
           PrintF(out, " (field at offset %d)\n", index);
           break;
         }