Decouple root visitors from object visitors.

src/v8.gyp

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 1327 matching lines @@
         'v8.cc',
         'v8.h',
         'v8memory.h',
         'v8threads.cc',
         'v8threads.h',
         'value-serializer.cc',
         'value-serializer.h',
         'vector.h',
         'version.cc',
         'version.h',
+        'visitors.cc',
+        'visitors.h',
         'vm-state-inl.h',
         'vm-state.h',
         'wasm/decoder.h',
         'wasm/function-body-decoder.cc',
         'wasm/function-body-decoder.h',
         'wasm/function-body-decoder-impl.h',
         'wasm/leb-helper.h',
         'wasm/module-decoder.cc',
         'wasm/module-decoder.h',
         'wasm/signature-map.cc',
@@ skipping 1129 matching lines @@
         }],
         ['want_separate_host_toolset==1', {
           'toolsets': ['host'],
         }, {
           'toolsets': ['target'],
         }],
       ],
     },
   ],
 }