[serializer] prepare attached references for general use.

src/snapshot/startup-serializer.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/snapshot/startup-serializer.h"
 
 #include "src/objects-inl.h"
 #include "src/v8threads.h"
 
 namespace v8 {
@@ skipping 55 matching lines @@
   // Object has not yet been serialized.  Serialize it here.
   ObjectSerializer object_serializer(this, obj, sink_, how_to_code,
                                      where_to_point);
   object_serializer.Serialize();
 
   if (serializing_immortal_immovables_roots_ &&
       root_index != RootIndexMap::kInvalidRootIndex) {
     // Make sure that the immortal immovable root has been included in the first
     // chunk of its reserved space , so that it is deserialized onto the first
     // page of its space and stays immortal immovable.
-    BackReference ref = back_reference_map_.Lookup(obj);
-    CHECK(ref.is_valid() && ref.chunk_index() == 0);
+    SerializerReference ref = reference_map_.Lookup(obj);
+    CHECK(ref.is_back_reference() && ref.chunk_index() == 0);
   }
 }
 
 void StartupSerializer::SerializeWeakReferencesAndDeferred() {
   // This comes right after serialization of the partial snapshot, where we
   // add entries to the partial snapshot cache of the startup snapshot. Add
   // one entry with 'undefined' to terminate the partial snapshot cache.
   Object* undefined = isolate()->heap()->undefined_value();
   VisitPointer(&undefined);
   isolate()->heap()->IterateWeakRoots(this, VISIT_ALL);
@@ skipping 70 matching lines @@
   if (root_index == Heap::kStackLimitRootIndex ||
       root_index == Heap::kRealStackLimitRootIndex) {
     return true;
   }
   return Heap::RootIsImmortalImmovable(root_index) !=
          serializing_immortal_immovables_roots_;
 }
 
 }  // namespace internal
 }  // namespace v8