The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0492d934bfa096c4b26ea03014510d9bc09e15aa

commit 0492d934bfa096c4b26ea03014510d9bc09e15aa
Author: Yao Xiao <yaoxia@chromium.org>
Date: Thu Jan 10 17:37:36 2019

Fix UseCounter DownloadInSandbox for mainframe download

We were not recording UseCounter DownloadInSandbox for navigation download in
sandboxed mainframe. This CL fixes the case where the download happens in a RFH
that has at least a committed load.

A separate CL will be addressing the case for a popup to a download where there
hasn't been a commit, in which case we might want to / have to record the
UseCounter in the opener page. Currently for this siutation, no UseCounter will
be recorded.

This CL also adds the sandbox bit to the mainframe download UMA/UKM.

Bug: 917082
Change-Id: If61a87f8e12c1e6c756a79da02f2f92f0cb4f5cb
Reviewed-on: https://chromium-review.googlesource.com/c/1383713
Commit-Queue: Yao Xiao <yaoxia@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621623}
[modify] https://crrev.com/0492d934bfa096c4b26ea03014510d9bc09e15aa/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer.cc
[modify] https://crrev.com/0492d934bfa096c4b26ea03014510d9bc09e15aa/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer_browsertest.cc
[modify] https://crrev.com/0492d934bfa096c4b26ea03014510d9bc09e15aa/third_party/blink/common/download/download_stats.cc
[modify] https://crrev.com/0492d934bfa096c4b26ea03014510d9bc09e15aa/third_party/blink/public/common/download/download_stats.h
[modify] https://crrev.com/0492d934bfa096c4b26ea03014510d9bc09e15aa/third_party/blink/renderer/core/html/html_anchor_element.cc
[modify] https://crrev.com/0492d934bfa096c4b26ea03014510d9bc09e15aa/tools/metrics/histograms/enums.xml
[modify] https://crrev.com/0492d934bfa096c4b26ea03014510d9bc09e15aa/tools/metrics/histograms/histograms.xml
[modify] https://crrev.com/0492d934bfa096c4b26ea03014510d9bc09e15aa/tools/metrics/ukm/ukm.xml