Fix trivial error in Firefogg upload handling

Basically, we fire the handlers before the uploads have the files in the
inputs for some reason, so now we need to handle providedFile and file
as well as the inputs. In fact, I'm not totally sure those file inputs
*ever* get the file data, so this can't ever have worked.

Bug: 69374
Change-Id: I8d1ecca8f5858ed421066fa0de2e088b9b00810c