Make incremental marker post-process JSWeakCollection.

test/cctest/test-weakmaps.cc

Index: test/cctest/test-weakmaps.cc
diff --git a/test/cctest/test-weakmaps.cc b/test/cctest/test-weakmaps.cc
index 369dae5e999f91205b5e877283cd318b9e09ee6d..2684deb4158efba23712c73c90be81d80cd857bb 100644
--- a/test/cctest/test-weakmaps.cc
+++ b/test/cctest/test-weakmaps.cc
@@ -46,10 +46,12 @@ static Handle<JSWeakMap> AllocateJSWeakMap(Isolate* isolate) {
   Handle<Map> map = factory->NewMap(JS_WEAK_MAP_TYPE, JSWeakMap::kSize);
   Handle<JSObject> weakmap_obj = factory->NewJSObjectFromMap(map);
   Handle<JSWeakMap> weakmap(JSWeakMap::cast(*weakmap_obj));
-  // Do not use handles for the hash table, it would make entries strong.
-  Handle<ObjectHashTable> table = ObjectHashTable::New(isolate, 1);
-  weakmap->set_table(*table);
-  weakmap->set_next(Smi::FromInt(0));
+  // Do not leak handles for the hash table, it would make entries strong.
+  {
+    HandleScope scope(isolate);
+    Handle<ObjectHashTable> table = ObjectHashTable::New(isolate, 1);
+    weakmap->set_table(*table);
+  }
   return weakmap;
 }