Decouple root visitors from object visitors.

test/cctest/heap/test-heap.cc

Index: test/cctest/heap/test-heap.cc
diff --git a/test/cctest/heap/test-heap.cc b/test/cctest/heap/test-heap.cc
index baef3c98a6cf434075c1f58f6e55d8fdad796d14..9159d5cfaa0a04813af8553edf70f2ab1df1e6cc 100644
--- a/test/cctest/heap/test-heap.cc
+++ b/test/cctest/heap/test-heap.cc
@@ -4178,10 +4178,9 @@ TEST(LargeObjectSlotRecording) {
   }
 }
 
-
-class DummyVisitor : public ObjectVisitor {
+class DummyVisitor : public RootVisitor {
  public:
-  void VisitPointers(Object** start, Object** end) override {}
+  void VisitRootPointers(Root root, Object** start, Object** end) override {}
 };