Fix crash when user closes window prior to the "Confirm Install" prompt showing

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 358 matching lines @@
       'browser/extensions/extension_bindings_apitest.cc',
       '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_ui_browsertest.cc',
       'browser/extensions/extension_javascript_url_apitest.cc',
       'browser/extensions/extension_loading_browsertest.cc',
       'browser/extensions/extension_messages_apitest.cc',
       'browser/extensions/extension_override_apitest.cc',
       'browser/extensions/extension_resource_request_policy_apitest.cc',
       'browser/extensions/extension_startup_browsertest.cc',
       'browser/extensions/extension_storage_apitest.cc',
       'browser/extensions/extension_storage_monitor_browsertest.cc',
       'browser/extensions/extension_tabs_apitest.cc',
@@ skipping 2778 matching lines @@
             ['enable_webrtc==1', {
               'dependencies': [
                 '../third_party/libjingle/libjingle.gyp:libjingle_webrtc'
               ]
             }],
           ],
         }]
     }],
   ],  # 'conditions'
 }