[heap] Move slots buffer into a separate file.

BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
 # Because standalone V8 builds are not supported, assume this is part of a
@@ skipping 969 matching lines @@
     "src/heap/memory-reducer.cc",
     "src/heap/memory-reducer.h",
     "src/heap/object-stats.cc",
     "src/heap/object-stats.h",
     "src/heap/objects-visiting-inl.h",
     "src/heap/objects-visiting.cc",
     "src/heap/objects-visiting.h",
     "src/heap/scavenger-inl.h",
     "src/heap/scavenger.cc",
     "src/heap/scavenger.h",
+    "src/heap/slots-buffer.cc",
+    "src/heap/slots-buffer.h",
     "src/heap/spaces-inl.h",
     "src/heap/spaces.cc",
     "src/heap/spaces.h",
     "src/heap/store-buffer-inl.h",
     "src/heap/store-buffer.cc",
     "src/heap/store-buffer.h",
     "src/hydrogen-alias-analysis.h",
     "src/hydrogen-bce.cc",
     "src/hydrogen-bce.h",
     "src/hydrogen-bch.cc",
@@ skipping 865 matching lines @@
     if (!is_component_build) {
       sources += [
         "$target_gen_dir/d8-js.cc",
       ]
     }
     if (v8_enable_i18n_support) {
       deps += [ "//third_party/icu" ]
     }
   }
 }