For HashTable-backed JS objects, use the proper type in the table() accessor

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 869b318f547572257b66beb0df92c9e32b2ed814..e093b1850d713346af0028b560e2278d748ca0eb 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -1324,11 +1324,10 @@ class MarkCompactMarkingVisitor
         object_size);
 
     // Mark the backing hash table without pushing it on the marking stack.
-    Object* table_object = weak_map->table();
-    if (!table_object->IsHashTable()) return;
-    ObjectHashTable* table = ObjectHashTable::cast(table_object);
     Object** table_slot =
         HeapObject::RawField(weak_map, JSWeakMap::kTableOffset);
+    if (!(*table_slot)->IsHashTable()) return;
+    ObjectHashTable* table = ObjectHashTable::cast(*table_slot);
     MarkBit table_mark = Marking::MarkBitFrom(table);
     collector->RecordSlot(table_slot, table_slot, table);
     if (!table_mark.Get()) collector->SetMark(table, table_mark);
@@ -2411,7 +2410,7 @@ void MarkCompactCollector::ProcessWeakMaps() {
   while (weak_map_obj != Smi::FromInt(0)) {
     ASSERT(MarkCompactCollector::IsMarked(HeapObject::cast(weak_map_obj)));
     JSWeakMap* weak_map = reinterpret_cast<JSWeakMap*>(weak_map_obj);
-    ObjectHashTable* table = ObjectHashTable::cast(weak_map->table());
+    ObjectHashTable* table = weak_map->table();
     Object** anchor = reinterpret_cast<Object**>(table->address());
     for (int i = 0; i < table->Capacity(); i++) {
       if (MarkCompactCollector::IsMarked(HeapObject::cast(table->KeyAt(i)))) {
@@ -2436,7 +2435,7 @@ void MarkCompactCollector::ClearWeakMaps() {
   while (weak_map_obj != Smi::FromInt(0)) {
     ASSERT(MarkCompactCollector::IsMarked(HeapObject::cast(weak_map_obj)));
     JSWeakMap* weak_map = reinterpret_cast<JSWeakMap*>(weak_map_obj);
-    ObjectHashTable* table = ObjectHashTable::cast(weak_map->table());
+    ObjectHashTable* table = weak_map->table();
     for (int i = 0; i < table->Capacity(); i++) {
       if (!MarkCompactCollector::IsMarked(HeapObject::cast(table->KeyAt(i)))) {
         table->RemoveEntry(i);