[File Manager] Always open as window.

chrome/browser/resources/file_manager/manifest.json

 {
   // chrome-extension://hhaomjibdihmijegdhdafkllkbggdgoj/
   "key": "MIGdMA0GCSqGSIb3DQEBAQUAA4GLADCBhwKBgQDlhpGghtnNJ7pluQN0RDwbUxwwi99oM35ZEaFYvxPLrf0fIEC18cfDdJi6u4aJ+UoSpgzK731L0P/k4LvK2Rz9kVKOy0+IvuRrWkT7lbrLfA1UEBh02OA1AAshjmyRg4IxCqgl8ia8XWq6HKegS1y1KXZYGgb4qp7Bh9VC4cIzswIBIw==",
   "name": "Files",
   "version": "0.1",
   "description": "File Manager",
   "incognito" : "split",
   "icons": {
     "16": "images/icon16.png",
     "128": "images/icon128.png"
   },
   "permissions": [
     "fileBrowserHandler",
     "fileBrowserPrivate",
     "mediaPlayerPrivate",
     "metricsPrivate",
     "unlimitedStorage",
     "chrome://extension-icon/",
     "chrome://resources/",
     "tabs",
     "clipboardWrite",
     "clipboardRead",
     "https://*.googleusercontent.com/"
   ],
   "content_security_policy": "default-src 'none'; script-src 'self'; style-src 'self' 'unsafe-inline'; frame-src 'self' about:; img-src 'self' data: filesystem: https://docs.google.com https://*.googleusercontent.com chrome://extension-icon; media-src filesystem: https://*.googleusercontent.com;",
   "app": {
     "launch": {
+      "container": "panel",
       "local_path": "main.html"
     }
   },
   "file_browser_handlers": [
     {
       "id": "play",
       "default_title": "__MSG_PLAY_MEDIA__",
       "default_icon": "images/filetype_audio.png",
       "file_filters": [
         "filesystem:*.flac",
@@ skipping 105 matching lines @@
         "filesystem:*.gslides",
         "filesystem:*.gdraw",
         "filesystem:*.gtable"
       ]
     }
   ],
   "chrome_url_overrides": {
     "files": "main.html"
   }
 }