image-burner: Update image burner file management to use base::File

Replace image burner file management classes to use Chrome base file
utilities. This also fixes determining source file size when file size
overflows int (on 32 bit systems).

BUG=chromium:644547
TEST=ran chrome recovery utility

Change-Id: I33f174d0361fe077f09c0746bb103f0d936e7ffe
Reviewed-on: https://chromium-review.googlesource.com/383842
Commit-Ready: Toni Barzic <tbarzic@chromium.org>
Tested-by: Toni Barzic <tbarzic@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
6 files changed