Decouple root visitors from object visitors.

src/snapshot/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_SERIALIZER_H_
 #define V8_SNAPSHOT_SERIALIZER_H_
 
 #include "src/isolate.h"
 #include "src/log.h"
 #include "src/objects.h"
@@ skipping 138 matching lines @@
     }
 
    private:
     static const int kMaxRecursionDepth = 32;
     Serializer* serializer_;
   };
 
   virtual void SerializeObject(HeapObject* o, HowToCode how_to_code,
                                WhereToPoint where_to_point, int skip) = 0;
 
-  void VisitPointers(Object** start, Object** end) override;
+  void VisitRootPointers(Root root, Object** start, Object** end) override;
 
   void PutRoot(int index, HeapObject* object, HowToCode how, WhereToPoint where,
                int skip);
 
   void PutSmi(Smi* smi);
 
   void PutBackReference(HeapObject* object, SerializerReference reference);
 
   void PutAttachedReference(SerializerReference reference,
                             HowToCode how_to_code, WhereToPoint where_to_point);
@@ skipping 144 matching lines @@
   SnapshotByteSink* sink_;
   int reference_representation_;
   int bytes_processed_so_far_;
   bool code_has_been_output_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_SNAPSHOT_SERIALIZER_H_