Loading blob resource url in to chrome extension

i want to make a chrome extension which download a image from web page, src of image is blob url. when i am trying to make xmlhttp request on blob url through extension i am unable to access blob url i am getting following error

There were warnings when trying to install this extension:
Permission ‘blob:https://web.whatsapp.com/d6b0a8f3-9f38-4588-9f0a-e11ff9989452‘ is unknown or URL pattern is malformed.

how to give permission to access a blob url through chrome extension.