[base] Move hashmap allocator to a field

src/zone.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ZONE_H_
 #define V8_ZONE_H_
 
 #include <limits>
 
 #include "src/base/accounting-allocator.h"
@@ skipping 140 matching lines @@
 
   Zone* zone() const { return zone_; }
 
  private:
   Zone* zone_;
 };
 
 
 // The ZoneAllocationPolicy is used to specialize generic data
 // structures to allocate themselves and their elements in the Zone.
-class ZoneAllocationPolicy final {
+class ZoneAllocationPolicy {
  public:
   explicit ZoneAllocationPolicy(Zone* zone) : zone_(zone) { }
   void* New(size_t size) { return zone()->New(size); }
   static void Delete(void* pointer) {}
   Zone* zone() const { return zone_; }
 
  private:
   Zone* zone_;
 };
 
@@ skipping 72 matching lines @@
   void operator delete(void* pointer, Zone* zone) { UNREACHABLE(); }
 };
 
 typedef base::TemplateHashMapImpl<void*, void*, ZoneAllocationPolicy>
     ZoneHashMap;
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ZONE_H_