VisitObject should use MarkObject.

BUG=

Review URL: https://codereview.chromium.org/1151993005

Cr-Commit-Position: refs/heads/master@{#28781}

src/heap/incremental-marking.cc

@@ -629,10 +629,7 @@ void IncrementalMarking::UpdateMarkingDequeAfterScavenge() {
 
 
 void IncrementalMarking::VisitObject(Map* map, HeapObject* obj, int size) {
-  MarkBit map_mark_bit = Marking::MarkBitFrom(map);
-  if (Marking::IsWhite(map_mark_bit)) {
-    WhiteToGreyAndPush(map, map_mark_bit);
-  }
+  MarkObject(heap_, map);
 
   IncrementalMarkingMarkingVisitor::IterateBody(map, obj);