Make incremental marker post-process JSWeakCollection.

src/objects-visiting-inl.h

Index: src/objects-visiting-inl.h
diff --git a/src/objects-visiting-inl.h b/src/objects-visiting-inl.h
index 7ed0e4abda063c69602bfe9d977695e8e67c5bca..65c93a288bfb553ed792013c185b3896675e26d0 100644
--- a/src/objects-visiting-inl.h
+++ b/src/objects-visiting-inl.h
@@ -66,9 +66,7 @@ void StaticNewSpaceVisitor<StaticVisitor>::Initialize() {
 
   table_.Register(kVisitFreeSpace, &VisitFreeSpace);
 
-  table_.Register(kVisitJSWeakMap, &JSObjectVisitor::Visit);
-
-  table_.Register(kVisitJSWeakSet, &JSObjectVisitor::Visit);
+  table_.Register(kVisitJSWeakCollection, &JSObjectVisitor::Visit);
 
   table_.Register(kVisitJSRegExp, &JSObjectVisitor::Visit);
 
@@ -182,9 +180,7 @@ void StaticMarkingVisitor<StaticVisitor>::Initialize() {
 
   table_.Register(kVisitSeqTwoByteString, &DataObjectVisitor::Visit);
 
-  table_.Register(kVisitJSWeakMap, &StaticVisitor::VisitWeakCollection);
-
-  table_.Register(kVisitJSWeakSet, &StaticVisitor::VisitWeakCollection);
+  table_.Register(kVisitJSWeakCollection, &VisitWeakCollection);
 
   table_.Register(kVisitOddball,
                   &FixedBodyVisitor<StaticVisitor,
@@ -286,7 +282,6 @@ void StaticMarkingVisitor<StaticVisitor>::VisitCodeTarget(
   // Monomorphic ICs are preserved when possible, but need to be flushed
   // when they might be keeping a Context alive, or when the heap is about
   // to be serialized.
-
   if (FLAG_cleanup_code_caches_at_gc && target->is_inline_cache_stub()
       && (target->ic_state() == MEGAMORPHIC || target->ic_state() == GENERIC ||
           target->ic_state() == POLYMORPHIC || heap->flush_monomorphic_ics() ||
@@ -402,6 +397,40 @@ void StaticMarkingVisitor<StaticVisitor>::VisitAllocationSite(
 
 
 template<typename StaticVisitor>
+void StaticMarkingVisitor<StaticVisitor>::VisitWeakCollection(
+    Map* map, HeapObject* object) {
+  Heap* heap = map->GetHeap();
+  JSWeakCollection* weak_collection =
+      reinterpret_cast<JSWeakCollection*>(object);
+  MarkCompactCollector* collector = heap->mark_compact_collector();
+
+  // Enqueue weak map in linked list of encountered weak maps.
+  if (weak_collection->next() == heap->undefined_value()) {
+    weak_collection->set_next(collector->encountered_weak_collections());
+    collector->set_encountered_weak_collections(weak_collection);
+  }
+
+  // Skip visiting the backing hash table containing the mappings and the
+  // pointer to the other enqueued weak collections, both are post-processed.
+  StaticVisitor::VisitPointers(heap,
+      HeapObject::RawField(object, JSWeakCollection::kPropertiesOffset),
+      HeapObject::RawField(object, JSWeakCollection::kTableOffset));
+  STATIC_ASSERT(JSWeakCollection::kTableOffset + kPointerSize ==
+      JSWeakCollection::kNextOffset);
+  STATIC_ASSERT(JSWeakCollection::kNextOffset + kPointerSize ==
+      JSWeakCollection::kSize);
+
+  if (!weak_collection->table()->IsHashTable()) return;
+
+  // Mark the backing hash table without pushing it on the marking stack.
+  Object** slot = HeapObject::RawField(object, JSWeakCollection::kTableOffset);
+  HeapObject* obj = HeapObject::cast(*slot);
+  heap->mark_compact_collector()->RecordSlot(slot, slot, obj);
+  StaticVisitor::MarkObjectWithoutPush(heap, obj);
+}
+
+
+template<typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitCode(
     Map* map, HeapObject* object) {
   Heap* heap = map->GetHeap();