The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e6fb7a00ac6edaa1090d15fd2e70dc129385fa83

commit e6fb7a00ac6edaa1090d15fd2e70dc129385fa83
Author: Yao Xiao <yaoxia@chromium.org>
Date: Wed Dec 12 20:32:09 2018

Add UseCounter for download in AdFrame

Bug: 911674
Change-Id: Ia010b625ed72ca575fc1aeafdf64990bcd2171d8
Reviewed-on: https://chromium-review.googlesource.com/c/1366766
Commit-Queue: Yao Xiao <yaoxia@chromium.org>
Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616021}
[modify] https://crrev.com/e6fb7a00ac6edaa1090d15fd2e70dc129385fa83/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer.cc
[modify] https://crrev.com/e6fb7a00ac6edaa1090d15fd2e70dc129385fa83/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer_browsertest.cc
[modify] https://crrev.com/e6fb7a00ac6edaa1090d15fd2e70dc129385fa83/chrome/browser/page_load_metrics/observers/use_counter/ukm_features.cc
[modify] https://crrev.com/e6fb7a00ac6edaa1090d15fd2e70dc129385fa83/chrome/browser/page_load_metrics/page_load_metrics_test_waiter.cc
[modify] https://crrev.com/e6fb7a00ac6edaa1090d15fd2e70dc129385fa83/chrome/browser/page_load_metrics/page_load_metrics_test_waiter.h
[modify] https://crrev.com/e6fb7a00ac6edaa1090d15fd2e70dc129385fa83/third_party/blink/public/platform/web_feature.mojom
[modify] https://crrev.com/e6fb7a00ac6edaa1090d15fd2e70dc129385fa83/third_party/blink/renderer/core/html/html_anchor_element.cc
[modify] https://crrev.com/e6fb7a00ac6edaa1090d15fd2e70dc129385fa83/tools/metrics/histograms/enums.xml