Reland: Templatize visitor arguments for TraceTrait mark and trace methods.

Source/wtf/HashTable.h

Index: Source/wtf/HashTable.h
diff --git a/Source/wtf/HashTable.h b/Source/wtf/HashTable.h
index 72099fdee50b4164cd409399a79f3e98a18a4ff9..d0e3ead6449c82e1662400532e4aae7bb64d6758 100644
--- a/Source/wtf/HashTable.h
+++ b/Source/wtf/HashTable.h
@@ -479,7 +479,7 @@ namespace WTF {
         template<typename HashTranslator, typename T> ValueType* lookup(T);
         template<typename HashTranslator, typename T> const ValueType* lookup(T) const;
 
-        void trace(typename Allocator::Visitor*);
+        template<typename VisitorDispatcher> void trace(VisitorDispatcher);
 
 #if ENABLE(ASSERT)
         int64_t modifications() const { return m_modifications; }
@@ -1223,7 +1223,8 @@ namespace WTF {
     };
 
     template<typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits, typename Allocator>
-    void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::trace(typename Allocator::Visitor* visitor)
+    template<typename VisitorDispatcher>
+    void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits, Allocator>::trace(VisitorDispatcher visitor)
     {
         // If someone else already marked the backing and queued up the trace
         // and/or weak callback then we are done. This optimization does not
@@ -1274,7 +1275,7 @@ namespace WTF {
             }
             for (ValueType* element = m_table + m_tableSize - 1; element >= m_table; element--) {
                 if (!isEmptyOrDeletedBucket(*element))
-                    Allocator::template trace<ValueType, Traits>(visitor, *element);
+                    Allocator::template trace<VisitorDispatcher, ValueType, Traits>(visitor, *element);
             }
         }
     }