Re-land alexbost's experimental offscreenTabs API.

chrome/chrome_tests.gypi

 # Copyright (c) 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' : {
     'pyautolib_sources': [
       'app/chrome_command_ids.h',
       'app/chrome_dll_resource.h',
       'common/automation_constants.h',
       'common/pref_names.cc',
@@ skipping 2529 matching lines @@
         'browser/custom_handlers/protocol_handler_registry_browsertest.cc',
         'browser/download/download_browsertest.cc',
         'browser/download/download_extension_apitest.cc',
         'browser/download/download_extension_test.cc',
         'browser/download/download_test_observer.cc',
         'browser/download/save_page_browsertest.cc',
         'browser/errorpage_browsertest.cc',
         'browser/extensions/alert_apitest.cc',
         'browser/extensions/all_urls_apitest.cc',
         'browser/extensions/api/dns/dns_apitest.cc',
+        'browser/extensions/api/offscreen_tabs/offscreen_tabs_apitest.cc',
         'browser/extensions/api/permissions/permissions_apitest.cc',
         'browser/extensions/api/serial/serial_apitest.cc',
         'browser/extensions/api/socket/socket_apitest.cc',
         'browser/extensions/api/terminal/terminal_private_apitest.cc',
         'browser/extensions/api/webrequest/webrequest_apitest.cc',
         'browser/extensions/app_background_page_apitest.cc',
         'browser/extensions/app_notification_browsertest.cc',
         'browser/extensions/app_process_apitest.cc',
         'browser/extensions/autoupdate_interceptor.cc',
         'browser/extensions/autoupdate_interceptor.h',
@@ skipping 2074 matching lines @@
               # Use outputs of this action as inputs for the main target build.
               # Seems as a misnomer but makes this happy on Linux (scons).
               'process_outputs_as_sources': 1,
             },
           ],  # 'actions'
         },
       ]
     }],  # 'coverage!=0'
   ],  # 'conditions'
 }