GN: Only have one gfx_x11 target

ui/gfx/x/gfx_x11.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
     'use_x11': 1,  # It is necessary to explicitly set use_x11 here to make sure
                    # that the exclusion rules in filename_rules.gypi do not
                    # exclude the x11* files.
   },
 
   'targets': [
     {
+      # GN version: //ui/gfx/x
       'target_name': 'gfx_x11',
       'type': '<(component)',
       'dependencies': [
         '../../../base/base.gyp:base',
         '../../../build/linux/system.gyp:x11',
       ],
       'defines': [
         'GFX_IMPLEMENTATION',
       ],
       'sources': [
         'x11_atom_cache.cc',
         'x11_atom_cache.h',
         'x11_connection.cc',
         'x11_connection.h',
         'x11_error_tracker.cc',
         'x11_error_tracker.h',
         'x11_switches.cc',
         'x11_switches.h',
         'x11_types.cc',
         'x11_types.h',
       ],
     },
   ]
 }