Use a plain FixedArray rather than a SeededNumberDictionary for ValueDeserializer::id_map_.

src/value-serializer.h

 // Copyright 2016 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_VALUE_SERIALIZER_H_
 #define V8_VALUE_SERIALIZER_H_
 
 #include <cstdint>
 #include <vector>
 
@@ skipping 235 matching lines @@
 
   Isolate* const isolate_;
   v8::ValueDeserializer::Delegate* const delegate_;
   const uint8_t* position_;
   const uint8_t* const end_;
   PretenureFlag pretenure_;
   uint32_t version_ = 0;
   uint32_t next_id_ = 0;
 
   // Always global handles.
-  Handle<SeededNumberDictionary> id_map_;
+  Handle<FixedArray> id_map_;
   MaybeHandle<SeededNumberDictionary> array_buffer_transfer_map_;
 
   DISALLOW_COPY_AND_ASSIGN(ValueDeserializer);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_VALUE_SERIALIZER_H_