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 6e1a4ecf2e0695cd32baf9dec9cd71e8e3f9ad37..e4acac031a5d045adc7e70098d4e55770e96af20 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -687,13 +687,12 @@ class MarkCompactCollector final : public MarkCompactCollectorBase {
   //    - 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();