I\'ve got a hidden file input field like this:
To add on user2355213s answer for the more current releases of protractor. ptor is obsolote and instead browser should be used. Also, executeScript() expects a string as parameter. So I ended up using
browser.executeScript('$(\'input[type="file"]\').attr("style", "");');
as my visibility setting was directly applied to the element. Of course, you can also use
browser.executeScript('$(\'input[type="file"]\').removeClass("hidden-uploader");');
depending on your HTML/CSS.