Merge V8 5.2.361.47  DO NOT MERGE

https://chromium.googlesource.com/v8/v8/+/5.2.361.47

FPIIM-449

Change-Id: Ibec421b85a9b88cb3a432ada642e469fe7e78346
(cherry picked from commit bcf72ee8e3b26f1d0726869c7ddb3921c68b09a8)
diff --git a/src/snapshot/startup-serializer.cc b/src/snapshot/startup-serializer.cc
index fab01f5..c3f9b3e 100644
--- a/src/snapshot/startup-serializer.cc
+++ b/src/snapshot/startup-serializer.cc
@@ -73,8 +73,8 @@
     // 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);
   }
 }