[heap] Implement concurrent marking boilerplate.

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 915 matching lines @@
         'globals.h',
         'handles-inl.h',
         'handles.cc',
         'handles.h',
         'heap-symbols.h',
         'heap/array-buffer-tracker-inl.h',
         'heap/array-buffer-tracker.cc',
         'heap/array-buffer-tracker.h',
         'heap/code-stats.cc',
         'heap/code-stats.h',
+        'heap/concurrent-marking.cc',
+        'heap/concurrent-marking.h',
         'heap/embedder-tracing.cc',
         'heap/embedder-tracing.h',
         'heap/memory-reducer.cc',
         'heap/memory-reducer.h',
         'heap/gc-idle-time-handler.cc',
         'heap/gc-idle-time-handler.h',
         'heap/gc-tracer.cc',
         'heap/gc-tracer.h',
         'heap/heap-inl.h',
         'heap/heap.cc',
@@ skipping 1570 matching lines @@
       'conditions': [
         ['want_separate_host_toolset_mkpeephole==1', {
           'toolsets': ['host'],
         }, {
           'toolsets': ['target'],
         }],
       ],
     },
   ],
 }