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

src/snapshot/partial-serializer.cc

Index: src/snapshot/partial-serializer.cc
diff --git a/src/snapshot/partial-serializer.cc b/src/snapshot/partial-serializer.cc
index fc25191395cb9e363976ba2a8b3ed59edd270057..7347995881b7ad14bc58d19875eb5cf123e11b1f 100644
--- a/src/snapshot/partial-serializer.cc
+++ b/src/snapshot/partial-serializer.cc
@@ -10,9 +10,8 @@ namespace v8 {
 namespace internal {
 
 PartialSerializer::PartialSerializer(Isolate* isolate,
-                                     Serializer* startup_snapshot_serializer,
-                                     SnapshotByteSink* sink)
-    : Serializer(isolate, sink),
+                                     Serializer* startup_snapshot_serializer)
+    : Serializer(isolate),
       startup_serializer_(startup_snapshot_serializer),
       next_partial_cache_index_(0) {
   InitializeCodeAddressMap();
@@ -63,9 +62,9 @@ void PartialSerializer::SerializeObject(HeapObject* obj, HowToCode how_to_code,
     FlushSkip(skip);
 
     int cache_index = PartialSnapshotCacheIndex(obj);
-    sink_->Put(kPartialSnapshotCache + how_to_code + where_to_point,
-               "PartialSnapshotCache");
-    sink_->PutInt(cache_index, "partial_snapshot_cache_index");
+    sink_.Put(kPartialSnapshotCache + how_to_code + where_to_point,
+              "PartialSnapshotCache");
+    sink_.PutInt(cache_index, "partial_snapshot_cache_index");
     return;
   }
 
@@ -90,7 +89,7 @@ void PartialSerializer::SerializeObject(HeapObject* obj, HowToCode how_to_code,
   }
 
   // Object has not yet been serialized.  Serialize it here.
-  ObjectSerializer serializer(this, obj, sink_, how_to_code, where_to_point);
+  ObjectSerializer serializer(this, obj, &sink_, how_to_code, where_to_point);
   serializer.Serialize();
 }