Decouple root visitors from object visitors.

src/snapshot/partial-serializer.cc

Index: src/snapshot/partial-serializer.cc
diff --git a/src/snapshot/partial-serializer.cc b/src/snapshot/partial-serializer.cc
index 308d01eb75656a0274427d79494d91ba952f235c..d3e60e0e4e30273fc5482dc391996d5fbd47f545 100644
--- a/src/snapshot/partial-serializer.cc
+++ b/src/snapshot/partial-serializer.cc
@@ -41,7 +41,7 @@ void PartialSerializer::Serialize(Object** o, bool include_global_proxy) {
       context->set_math_random_cache(isolate_->heap()->undefined_value());
     }
   }
-  VisitPointer(o);
+  VisitRootPointer(Root::kPartialSnapshotCache, o);
   SerializeDeferredObjects();
   SerializeEmbedderFields();
   Pad();