Precache should cancel when there is user traffic

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 1025 matching lines @@
       'browser/password_manager/password_manager_infobar_delegate_android.h',
       'browser/password_manager/save_password_infobar_delegate_android.cc',
       'browser/password_manager/save_password_infobar_delegate_android.h',
       'browser/password_manager/update_password_infobar_delegate_android.cc',
       'browser/password_manager/update_password_infobar_delegate_android.h',
       'browser/permissions/permission_queue_controller.cc',
       'browser/permissions/permission_queue_controller.h',
       'browser/platform_util_android.cc',
       'browser/precache/precache_manager_factory.cc',
       'browser/precache/precache_manager_factory.h',
+      'browser/precache/precache_util.cc',
+      'browser/precache/precache_util.h',
       'browser/prerender/external_prerender_handler_android.cc',
       'browser/prerender/external_prerender_handler_android.h',
       'browser/profiles/profile_android.cc',
       'browser/profiles/profile_android.h',
       'browser/search/contextual_search_policy_handler_android.cc',
       'browser/search/contextual_search_policy_handler_android.h',
       'browser/signin/oauth2_token_service_delegate_android.cc',
       'browser/signin/oauth2_token_service_delegate_android.h',
       'browser/ssl/ssl_add_certificate_android.cc',
     ],
@@ skipping 3245 matching lines @@
             '../components/components.gyp:rlz',
             '../components/components.gyp:search_engines',
             '../rlz/rlz.gyp:rlz_lib',
             'common',
           ],
         },
       ],
     }],
   ],
 }