[heap] Move slots buffer into a separate file.

test/cctest/test-unboxed-doubles.cc

 // Copyright 2014 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 <stdlib.h>
 #include <utility>
 
 #include "src/v8.h"
 
 #include "src/compilation-cache.h"
 #include "src/execution.h"
 #include "src/factory.h"
 #include "src/global-handles.h"
+#include "src/heap/slots-buffer.h"
 #include "src/ic/ic.h"
 #include "src/macro-assembler.h"
 #include "test/cctest/cctest.h"
 #include "test/cctest/heap-tester.h"
 
 using namespace v8::base;
 using namespace v8::internal;
 
 #if V8_DOUBLE_FIELDS_UNBOXING
 
@@ skipping 1657 matching lines @@
 
 // TODO(ishell): add respective tests for property kind reconfiguring from
 // accessor field to double, once accessor fields are supported by
 // Map::ReconfigureProperty().
 
 
 // TODO(ishell): add respective tests for fast property removal case once
 // Map::ReconfigureProperty() supports that.
 
 #endif