Decouple root visitors from object visitors.

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index 2ebf4a720c19a5dd0e55779584f6d26039c7ab86..ed60c2bf1a70638454a86c20b50b74723ecd20f4 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -705,13 +705,12 @@ class MarkCompactCollector {
   //    - Processing of objects reachable through Harmony WeakMaps.
   //    - Objects reachable due to host application logic like object groups,
   //      implicit references' groups, or embedder heap tracing.
-  void ProcessEphemeralMarking(ObjectVisitor* visitor,
-                               bool only_process_harmony_weak_collections);
+  void ProcessEphemeralMarking(bool only_process_harmony_weak_collections);
 
   // If the call-site of the top optimized code was not prepared for
   // deoptimization, then treat the maps in the code as strong pointers,
   // otherwise a map can die and deoptimize the code.
-  void ProcessTopOptimizedFrame(ObjectVisitor* visitor);
+  void ProcessTopOptimizedFrame(RootMarkingVisitor* visitor);
 
   // Collects a list of dependent code from maps embedded in optimize code.
   DependentCode* DependentCodeListFromNonLiveMaps();