It looks like Facebook is testing a new way to encourage users to update their profile picture by adding “+ Make Profile Picture” button near to the photos.
As seen on the screenshot, the new button is placed directly above to the other buttons namely ‘Tag Photo’, ‘Add Location’ and ‘Edit’. Whenever the user clicks on “+ Make Profile Picture” it will opens up the crop tool. After cropping the desired area, clicking on the ‘Done Cropping’ will updates user’s profile picture to this new cropped one.
“+ Make Profile Picture” button is visible in all photo albums of the users including ‘Photos of You’, ‘Your Photos’, ‘Albums’ etc.
Actually this feature is already available to all users in the ‘Options’ menu in the photos.