ASSERT that Visitor::mark is only called when inGC()

Source/wtf/HashTable.h

Index: Source/wtf/HashTable.h
diff --git a/Source/wtf/HashTable.h b/Source/wtf/HashTable.h
index 40d57616b4d1fc2e4fc315c7d71174d774f49cbb..1924e891fddefb78e4ac17dc38bd6b038798148e 100644
--- a/Source/wtf/HashTable.h
+++ b/Source/wtf/HashTable.h
@@ -1256,7 +1256,19 @@ template<typename Key, typename Value, typename Extractor, typename HashFunction
                         // At this stage calling trace can make no difference
                         // (everything is already traced), but we use the
                         // return value to remove things from the collection.
-                        if (TraceInCollectionTrait<WeakHandlingInCollections, WeakPointersActWeak, ValueType, Traits>::trace(visitor, *element)) {
+
+                        // FIXME: This should be rewritten so that this can check
+                        // if the element is dead without calling trace,
+                        // which is semantically not correct to be called in
+                        // weak processing stage.
+#if ENABLE(ASSERT)
+                        visitor->setAllowMarkingForHashTableWeakProcessing(true);
+#endif
+                        bool elementIsDead = TraceInCollectionTrait<WeakHandlingInCollections, WeakPointersActWeak, ValueType, Traits>::trace(visitor, *element);
+#if ENABLE(ASSERT)
+                        visitor->setAllowMarkingForHashTableWeakProcessing(false);
+#endif
+                        if (elementIsDead) {
                             table->registerModification();
                             HashTableType::deleteBucket(*element); // Also calls the destructor.
                             table->m_deletedCount++;