GitLab

The progress_callback is already nullable, so it doesn't need to be
wrapped with base::Optional.

Bug: None
Change-Id: Ifb43c88ab59b2ec0208225359b11070407fc5912
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2442571Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Jesse Schettler <jschettler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813450}