[Extensions] Migrate ExtensionInstallPrompt::Delegate to be a callback

chrome/chrome_tests.gypi

 # Copyright 2013 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_browser_extensions_test_support_sources': [
       # A list of sources which is shared between different browser tests.
       'browser/apps/app_browsertest_util.cc',
       'browser/apps/app_browsertest_util.h',
       'browser/extensions/browsertest_util.cc',
@@ skipping 225 matching lines @@
       'browser/extensions/extension_context_menu_browsertest.cc',
       'browser/extensions/extension_disabled_ui_browsertest.cc',
       'browser/extensions/extension_dom_clipboard_apitest.cc',
       'browser/extensions/extension_fileapi_apitest.cc',
       'browser/extensions/extension_functional_browsertest.cc',
       'browser/extensions/extension_geolocation_apitest.cc',
       'browser/extensions/extension_get_views_apitest.cc',
       'browser/extensions/extension_icon_source_apitest.cc',
       'browser/extensions/extension_incognito_apitest.cc',
       'browser/extensions/extension_install_prompt_browsertest.cc',
+      'browser/extensions/extension_install_prompt_test_helper.cc',
+      'browser/extensions/extension_install_prompt_test_helper.h',
       'browser/extensions/extension_install_ui_browsertest.cc',
       'browser/extensions/extension_javascript_url_apitest.cc',
       'browser/extensions/extension_loading_browsertest.cc',
       'browser/extensions/extension_management_test_util.cc',
       'browser/extensions/extension_management_test_util.h',
       'browser/extensions/extension_messages_apitest.cc',
       'browser/extensions/extension_override_apitest.cc',
       'browser/extensions/extension_request_limiting_throttle_browsertest.cc',
       'browser/extensions/extension_resource_request_policy_apitest.cc',
       'browser/extensions/extension_startup_browsertest.cc',
@@ skipping 3276 matching lines @@
             'utility',
           ],
           'sources': [
             'tools/service_discovery_sniffer/service_discovery_sniffer.cc',
             'tools/service_discovery_sniffer/service_discovery_sniffer.h',
           ],
         }]
     }],
   ],  # 'conditions'
 }