[snapshot] make snapshot sink a non-dynamic member of the serializer.

src/snapshot/partial-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_SNAPSHOT_PARTIAL_SERIALIZER_H_
 #define V8_SNAPSHOT_PARTIAL_SERIALIZER_H_
 
 #include "src/address-map.h"
 #include "src/snapshot/serializer.h"
 
 namespace v8 {
 namespace internal {
 
 class PartialSerializer : public Serializer {
  public:
-  PartialSerializer(Isolate* isolate, Serializer* startup_snapshot_serializer,
-                    SnapshotByteSink* sink);
+  PartialSerializer(Isolate* isolate, Serializer* startup_snapshot_serializer);
 
   ~PartialSerializer() override;
 
   // Serialize the objects reachable from a single object pointer.
   void Serialize(Object** o);
 
  private:
   class PartialCacheIndexMap : public AddressMapBase {
    public:
     PartialCacheIndexMap() : map_(base::HashMap::PointersMatch) {}
@@ skipping 24 matching lines @@
   Serializer* startup_serializer_;
   PartialCacheIndexMap partial_cache_index_map_;
   int next_partial_cache_index_;
   DISALLOW_COPY_AND_ASSIGN(PartialSerializer);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_SNAPSHOT_PARTIAL_SERIALIZER_H_