[heap] Move slots buffer into a separate file.

src/heap/spaces.cc

 // Copyright 2011 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.
 
 #include "src/heap/spaces.h"
 
 #include "src/base/bits.h"
 #include "src/base/platform/platform.h"
 #include "src/full-codegen/full-codegen.h"
-#include "src/heap/mark-compact.h"
+#include "src/heap/slots-buffer.h"
 #include "src/macro-assembler.h"
 #include "src/msan.h"
 #include "src/snapshot/snapshot.h"
 
 namespace v8 {
 namespace internal {
 
 
 // ----------------------------------------------------------------------------
 // HeapObjectIterator
@@ skipping 3164 matching lines @@
     object->ShortPrint();
     PrintF("\n");
   }
   printf(" --------------------------------------\n");
   printf(" Marked: %x, LiveCount: %x\n", mark_size, LiveBytes());
 }
 
 #endif  // DEBUG
 }  // namespace internal
 }  // namespace v8