Decouple root visitors from object visitors.

src/snapshot/serializer-common.cc

Index: src/snapshot/serializer-common.cc
diff --git a/src/snapshot/serializer-common.cc b/src/snapshot/serializer-common.cc
index 89aabdf263b3e70534a3c248ab9002134edbb88d..05a18ab727cc5c91445a98a8b9880d2bf81d515b 100644
--- a/src/snapshot/serializer-common.cc
+++ b/src/snapshot/serializer-common.cc
@@ -67,14 +67,14 @@ void SerializedData::AllocateData(int size) {
 //  - during normal GC to keep its content alive.
 //  - not during serialization. The partial serializer adds to it explicitly.
 DISABLE_CFI_PERF
-void SerializerDeserializer::Iterate(Isolate* isolate, ObjectVisitor* visitor) {
+void SerializerDeserializer::Iterate(Isolate* isolate, RootVisitor* visitor) {
   List<Object*>* cache = isolate->partial_snapshot_cache();
   for (int i = 0;; ++i) {
     // Extend the array ready to get a value when deserializing.
     if (cache->length() <= i) cache->Add(Smi::kZero);
     // During deserialization, the visitor populates the partial snapshot cache
     // and eventually terminates the cache with undefined.
-    visitor->VisitPointer(&cache->at(i));
+    visitor->VisitRootPointer(Root::kPartialSnapshotCache, &cache->at(i));
     if (cache->at(i)->IsUndefined(isolate)) break;
   }
 }