Cancelling an upload ended the loop like a normal finish, and the Files
app then reported every picked file as uploaded. Uploads now return how
many files went up and whether they were cancelled, so a cancel shows
"Upload canceled" (with the count of files that made it, if any).
Folder uploads also passed no cancel signal or progress callback to the
blob upload, so Cancel did not stop the file in flight and the progress
line stood still; they now behave like file uploads.
Linus Rath
e60840c0e6