[Files.app] Add tests of opening Gallery from Files.app

ui/file_manager/integration_tests/file_manager_test_manifest.json

 {
   // chrome-extension://hoobinhbdbiehknkpbpejbbpdbkdjmoco/
   "key": "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDBjsTE4ocXJWzgcCDCUcsPASoRCGaTHrHn6b4zDTCayTuJtyGKzw4xZPMiG4dbEbmSAwEU7UCoyJAM1XfLS7UQ/Zz7ft8wpZkSS8/PJW+E4Qu++tMS0csj2Wdrrd2c5yyWxlJ+H9o2ivwtwuxs7pd+LXt+gsBA0epnT04T9EvOTQIDAQAB",
   "name": "chrome file manager browser tests",
   "version": "0.1",
   "incognito": "split",  // Run a separate instance for the incognito mode.
   "manifest_version": 2,
   "background": {
     "scripts": [
       // List test_util.js and background.js first because the testcase
       // namespace is defined here.
       "test_util.js",
       "remote_call.js",
       "file_manager/background.js",
       "file_manager/copy_between_windows.js",
       "file_manager/create_new_folder.js",
       "file_manager/drive_specific.js",
       "file_manager/file_dialog.js",
       "file_manager/file_display.js",
       "file_manager/folder_shortcuts.js",
       "file_manager/grid_view.js",
       "file_manager/keyboard_operations.js",
       "file_manager/open_audio_files.js",
+      "file_manager/open_image_files.js",
       "file_manager/open_video_files.js",
       "file_manager/open_zip_files.js",
       "file_manager/restore_geometry.js",
       "file_manager/restore_prefs.js",
       "file_manager/share_dialog.js",
       "file_manager/suggest_app_dialog.js",
       "file_manager/tab_index.js",
       "file_manager/tasks.js",
       "file_manager/transfer.js",
       "file_manager/traverse.js"
     ]
   },
   "permissions": [
     "fileSystem",
     "tabs",
     "commandLinePrivate",
     "chrome-extension://oobinhbdbiehknkpbpejbbpdbkdjmoco/*",
     "chrome-extension://hhaomjibdihmijegdhdafkllkbggdgoj/*"
   ]
 }