On the Commons upload page there are these steps:
Some lack an abort button to cancel out, let's say if one realizes that one is about to upload the wrong picture!
For instance there is a button called Publish Files. Next to it should be another button called "cancel and abort upload".
Sure, you might say the user should just close the browser tab. But the user doesn't know what'll happen then. Perhaps the files with still be uploaded in some unnamed state.