Simplify checking for prefetch field trial in RDH

chrome/chrome_browser.gypi

 # Copyright 2012 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': {
     # All .cc, .h, .m, and .mm files under browser except for:
     # * tests and mocks.
     # * code below browser/chromeos
     # * code below browser/extensions
@@ skipping 410 matching lines @@
       'browser/page_load_metrics/page_load_metrics_initialize.h',
       'browser/performance_monitor/performance_monitor.cc',
       'browser/performance_monitor/performance_monitor.h',
       'browser/performance_monitor/process_metrics_history.cc',
       'browser/performance_monitor/process_metrics_history.h',
       'browser/platform_util.h',
       'browser/platform_util_chromeos.cc',
       'browser/platform_util_internal.h',
       'browser/platform_util_mac.mm',
       'browser/platform_util_win.cc',
-      'browser/prefetch/prefetch.cc',
-      'browser/prefetch/prefetch.h',
-      'browser/prefetch/prefetch_field_trial.cc',
-      'browser/prefetch/prefetch_field_trial.h',
       'browser/prerender/prerender_config.cc',
       'browser/prerender/prerender_config.h',
       'browser/prerender/prerender_contents.cc',
       'browser/prerender/prerender_contents.h',
       'browser/prerender/prerender_field_trial.cc',
       'browser/prerender/prerender_field_trial.h',
       'browser/prerender/prerender_final_status.cc',
       'browser/prerender/prerender_final_status.h',
       'browser/prerender/prerender_handle.cc',
       'browser/prerender/prerender_handle.h',
@@ skipping 3799 matching lines @@
             '../components/components.gyp:rlz',
             '../components/components.gyp:search_engines',
             '../rlz/rlz.gyp:rlz_lib',
             'common',
           ],
         },
       ],
     }],
   ],
 }