For Retried downloads, it's probably not a big deal, but it's often better to directly measure what you want, rather than try to compute it. It could maybe make sense to add a retry bucket to Download.Counts? Though probably not a big deal.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f27915a9950efbe08cae6cdde4efb1a4a9ddb2ab

commit f27915a9950efbe08cae6cdde4efb1a4a9ddb2ab
Author: Sidney San Martín <sdy@chromium.org>
Date: Tue Nov 21 18:15:30 2017

Add a stat for dragging a download from the shelf.

Bug:  783340 
Change-Id: I4b34e9d98627f49412bba3251820fa38445c5e63
Reviewed-on: https://chromium-review.googlesource.com/762667
Reviewed-by: Trent Apted <tapted@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Sidney San Martín <sdy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518306}
[modify] https://crrev.com/f27915a9950efbe08cae6cdde4efb1a4a9ddb2ab/chrome/browser/download/download_stats.cc
[modify] https://crrev.com/f27915a9950efbe08cae6cdde4efb1a4a9ddb2ab/chrome/browser/download/download_stats.h
[modify] https://crrev.com/f27915a9950efbe08cae6cdde4efb1a4a9ddb2ab/chrome/browser/ui/cocoa/download/download_item_button.mm
[modify] https://crrev.com/f27915a9950efbe08cae6cdde4efb1a4a9ddb2ab/chrome/browser/ui/cocoa/download/md_download_item_view.mm
[modify] https://crrev.com/f27915a9950efbe08cae6cdde4efb1a4a9ddb2ab/chrome/browser/ui/views/download/download_item_view.cc
[modify] https://crrev.com/f27915a9950efbe08cae6cdde4efb1a4a9ddb2ab/tools/metrics/histograms/enums.xml
[modify] https://crrev.com/f27915a9950efbe08cae6cdde4efb1a4a9ddb2ab/tools/metrics/histograms/histograms.xml

Renaming since discussion is happening in the launch bug.

jwd@/#3: Turns out there's a metric for that already, which I added to the launch bug (Download.Sources -> "Initiated by {Manual,Automatic} Resumption")!