Move map retaining to finalization of incremental marking.

test/cctest/test-heap.cc

Index: test/cctest/test-heap.cc
diff --git a/test/cctest/test-heap.cc b/test/cctest/test-heap.cc
index e52c0e4a1480244a2fc6cd2b6958f95e94798822..d30676c0d2bc1100e1540a1beb6a2945746d2cde 100644
--- a/test/cctest/test-heap.cc
+++ b/test/cctest/test-heap.cc
@@ -5822,9 +5822,13 @@ void CheckMapRetainingFor(int n) {
   Handle<WeakCell> weak_cell = AddRetainedMap(isolate, heap);
   CHECK(!weak_cell->cleared());
   for (int i = 0; i < n; i++) {
+    heap->StartIncrementalMarking();
+    SimulateIncrementalMarking(heap);
     heap->CollectGarbage(OLD_SPACE);
   }
   CHECK(!weak_cell->cleared());
+  heap->StartIncrementalMarking();
+  SimulateIncrementalMarking(heap);
   heap->CollectGarbage(OLD_SPACE);
   CHECK(weak_cell->cleared());
 }