[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
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@@ 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
+        # TODO: remove once chromium defines v8_tracing_include_dir
         '../..',
+        '<(v8_tracing_include_dir)',

[Michael Achenbach, 2016/06/15 06:42:43]

Won't that fail if you declare just in the standalone.gypi? Unless you define it
in chromium first...

[Mircea Trofin, 2016/06/15 06:45:53]

No, I left the ../.. Under the Todo. I like your idea better though - going
chrome first.

Then there's no need for the Todo here, nor the ../..

       ],
       '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'],
         }],
       ],
     },
   ],
 }