[heap] Separate scavenger functionality into own file.

src/heap/object-stats.h

 // Copyright 2015 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_HEAP_OBJECT_STATS_H_
 #define V8_HEAP_OBJECT_STATS_H_
 
 #include "src/heap/heap.h"
+#include "src/heap/objects-visiting.h"
 #include "src/objects.h"
 
 namespace v8 {
 namespace internal {
 
 class ObjectStats {
  public:
   explicit ObjectStats(Heap* heap) : heap_(heap) {}
 
   // ObjectStats are kept in two arrays, counts and sizes. Related stats are
@@ skipping 73 matching lines @@
                               FixedArraySubInstanceType dictionary_type);
 
   template <VisitorId id>
   static inline void Visit(Map* map, HeapObject* obj);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_OBJECT_STATS_H_