Move the check for fileBrowserHandler permission to FileBrowserHandler.

chrome/test/data/extensions/manifest_tests/filebrowser_invalid_access_permission.json

 {
   "name": "test",
   "version": "1",
+  "permissions": [
+    "fileBrowserHandler"
+  ],
   "file_browser_handlers": [
     {
       "id" : "ID",
       "default_title" : "Default title",
       "default_icon" : "icon.png",
       "file_filters" : [
         "filesystem:*.txt"
       ],
       "file_access": [ "read", "read@write" ]
     }
   ]
 }