Make incremental marker post-process JSWeakCollection.

test/cctest/test-weaksets.cc

Index: test/cctest/test-weaksets.cc
diff --git a/test/cctest/test-weaksets.cc b/test/cctest/test-weaksets.cc
index a83e16b12b6bb5a4f0b491ad3560ec4b17007e57..0e1ef17c05ce139d4baf4fc3c64d7a514d55687d 100644
--- a/test/cctest/test-weaksets.cc
+++ b/test/cctest/test-weaksets.cc
@@ -46,10 +46,12 @@ static Handle<JSWeakSet> AllocateJSWeakSet(Isolate* isolate) {
   Handle<Map> map = factory->NewMap(JS_WEAK_SET_TYPE, JSWeakSet::kSize);
   Handle<JSObject> weakset_obj = factory->NewJSObjectFromMap(map);
   Handle<JSWeakSet> weakset(JSWeakSet::cast(*weakset_obj));
-  // Do not use handles for the hash table, it would make entries strong.
-  Handle<ObjectHashTable> table = ObjectHashTable::New(isolate, 1);
-  weakset->set_table(*table);
-  weakset->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);
+    weakset->set_table(*table);
+  }
   return weakset;
 }