Revert of [Contextual Search] Remove opt-in code.

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 646 matching lines @@
       'browser/safe_browsing/srt_fetcher_win.cc',
       'browser/safe_browsing/srt_fetcher_win.h',
       'browser/safe_browsing/srt_field_trial_win.cc',
       'browser/safe_browsing/srt_field_trial_win.h',
       'browser/safe_browsing/srt_global_error_win.cc',
       'browser/safe_browsing/srt_global_error_win.h',
       'browser/safe_json_parser.cc',
       'browser/safe_json_parser.h',
       'browser/search/contextual_search_policy_handler_android.cc',
       'browser/search/contextual_search_policy_handler_android.h',
+      'browser/search/contextual_search_promo_source_android.cc',
+      'browser/search/contextual_search_promo_source_android.h',
       'browser/search/iframe_source.cc',
       'browser/search/iframe_source.h',
       'browser/search/instant_io_context.cc',
       'browser/search/instant_io_context.h',
       'browser/search/instant_service.cc',
       'browser/search/instant_service.h',
       'browser/search/instant_service_factory.cc',
       'browser/search/instant_service_factory.h',
       'browser/search/instant_service_observer.cc',
       'browser/search/instant_service_observer.h',
@@ skipping 3235 matching lines @@
           'variables': {
             'proto_in_dir': 'browser/sync_file_system/drive_backend',
             'proto_out_dir': 'chrome/browser/sync_file_system/drive_backend',
           },
           'includes': [ '../build/protoc.gypi' ]
         },
       ],
     },],
   ],
 }