[build] Provide tracing dependency via variable

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 369 matching lines @@
       'type': 'static_library',
       'dependencies': [
         'v8_libbase',
         'v8_libsampler',
       ],
       'variables': {
         'optimize': 'max',
       },
       'include_dirs+': [
         '..',
-        # To be able to find base/trace_event/common/trace_event_common.h
-        '../..',

[fmeawad, 2016/06/14 18:26:33]

This line was added to allow v8, when built inside chromium to be able to access
the chromium version of the file mentioned in the comment. Removing it would
break the chromium build AFAIK.

[fmeawad, 2016/06/14 20:06:27]

It was done this way because v8 inside chrome does not have any dependencies,
and to avoid cyclic dependencies.

       ],
       'sources': [  ### gcmole(all) ###
         '../include/v8-debug.h',
         '../include/v8-experimental.h',
         '../include/v8-platform.h',
         '../include/v8-profiler.h',
         '../include/v8-testing.h',
         '../include/v8-util.h',
         '../include/v8-version.h',
         '../include/v8.h',
@@ skipping 1878 matching lines @@
         }],
         ['want_separate_host_toolset==1', {
           'toolsets': ['host'],
         }, {
           'toolsets': ['target'],
         }],
       ],
     },
   ],
 }