Decouple root visitors from object visitors.

src/snapshot/serializer.cc

Index: src/snapshot/serializer.cc
diff --git a/src/snapshot/serializer.cc b/src/snapshot/serializer.cc
index e826a29fd32b282a12ff82b1572dc663f1377d09..a09ebae8018d9a6b9af239c9dbaa6efeb293cc7a 100644
--- a/src/snapshot/serializer.cc
+++ b/src/snapshot/serializer.cc
@@ -99,7 +99,7 @@ void Serializer::SerializeDeferredObjects() {
   sink_.Put(kSynchronize, "Finished with deferred objects");
 }
 
-void Serializer::VisitPointers(Object** start, Object** end) {
+void Serializer::VisitRootPointers(Root root, Object** start, Object** end) {
   for (Object** current = start; current < end; current++) {
     if ((*current)->IsSmi()) {
       PutSmi(Smi::cast(*current));