extensions: Abstract out install delay strategy

chrome/chrome_tests_unit.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': {
     'chrome_unit_tests_sources': [
       # histograms.xml is analyzed by AboutFlagsHistogramTest, so this
       # dependency is needed to make commit bots run unit_tests on
       # histograms.xml changes.
       '../tools/metrics/histograms/histograms.xml',
@@ skipping 520 matching lines @@
       'browser/extensions/pack_extension_unittest.cc',
       'browser/extensions/permission_message_combinations_unittest.cc',
       'browser/extensions/permission_messages_unittest.cc',
       'browser/extensions/permissions_based_management_policy_provider_unittest.cc',
       'browser/extensions/permissions_updater_unittest.cc',
       'browser/extensions/policy_handlers_unittest.cc',
       'browser/extensions/scripting_permissions_modifier_unittest.cc',
       'browser/extensions/shared_module_service_unittest.cc',
       'browser/extensions/standard_management_policy_provider_unittest.cc',
       'browser/extensions/token_cache/token_cache_service_unittest.cc',
+      'browser/extensions/update_install_delayer_unittest.cc',
       'browser/extensions/updater/extension_cache_fake.cc',
       'browser/extensions/updater/extension_cache_fake.h',
       'browser/extensions/updater/extension_updater_unittest.cc',
       'browser/extensions/user_script_listener_unittest.cc',
       'browser/extensions/warning_badge_service_unittest.cc',
       'browser/extensions/webstore_inline_installer_unittest.cc',
       'browser/extensions/webstore_installer_unittest.cc',
       'browser/extensions/zipfile_installer_unittest.cc',
       'browser/media/cast_transport_host_filter_unittest.cc',
       'browser/metrics/extensions_metrics_provider_unittest.cc',
@@ skipping 2453 matching lines @@
               'dependencies': [
                 '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
               ],
             }],
           ],
         },
       ],
     }],
   ],  # 'conditions'
 }