[serializer] Ensure immortal immovable roots are deserialized correctly.

src/address-map.cc

Index: src/address-map.cc
diff --git a/src/address-map.cc b/src/address-map.cc
index 681661af2978bbdcc78754a2f9e5a82e1dc9f46d..c154a9e54827813a815a312b654c7fb8645662b6 100644
--- a/src/address-map.cc
+++ b/src/address-map.cc
@@ -29,6 +29,11 @@ RootIndexMap::RootIndexMap(Isolate* isolate) {
       } else {
         SetValue(LookupEntry(map_, heap_object, true), i);
       }
+    } else {
+      // Immortal immovable root objects are constant and allocated on the first
+      // page of old space. Non-constant roots cannot be immortal immovable.
+      // The root index map contains all immortal immmovable root objects.
+      CHECK(!Heap::RootIsImmortalImmovable(root_index));

[Michael Starzinger, 2016/02/05 14:47:59]

I am not sure about this check. It only holds because we don't have e.g.
constant Smi entries in the root-set. Is this check really necessary to ensure
the invariant in question in the deserializer? Otherwise I would vote for
dropping this check.

     }
   }
   isolate->set_root_index_map(map_);