Introduce a field trial for Instant.

chrome/chrome_browser.gypi

 # Copyright (c) 2011 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.
 
 {
   'targets': [
     {
       'target_name': 'browser',
       'type': 'static_library',
       'dependencies': [
@@ skipping 1309 matching lines @@
         'browser/importer/toolbar_importer.cc',
         'browser/importer/toolbar_importer.h',
         'browser/importer/toolbar_importer_utils.cc',
         'browser/importer/toolbar_importer_utils.h',
         'browser/instant/instant_commit_type.h',
         'browser/instant/instant_confirm_dialog.cc',
         'browser/instant/instant_confirm_dialog.h',
         'browser/instant/instant_controller.cc',
         'browser/instant/instant_controller.h',
         'browser/instant/instant_delegate.h',
+        'browser/instant/instant_field_trial.cc',
+        'browser/instant/instant_field_trial.h',
         'browser/instant/instant_loader.cc',
         'browser/instant/instant_loader.h',
         'browser/instant/instant_loader_delegate.h',
         'browser/instant/instant_loader_manager.cc',
         'browser/instant/instant_loader_manager.h',
         'browser/instant/instant_unload_handler.cc',
         'browser/instant/instant_unload_handler.h',
         'browser/instant/promo_counter.cc',
         'browser/instant/promo_counter.h',
         'browser/internal_auth.cc',
@@ skipping 3489 matching lines @@
       ],
       'export_dependent_settings': [
         'in_memory_url_index_cache_proto',
       ],
       # This target exports a hard dependency because it includes generated
       # header files.
       'hard_dependency': 1,
     },
   ],
 }