The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a5f0c6cfea71ee9a8b8cfdd6b3d89d1b1bd3f980

commit a5f0c6cfea71ee9a8b8cfdd6b3d89d1b1bd3f980
Author: Varun Khaneja <vakh@chromium.org>
Date: Fri Sep 22 17:27:31 2017

Add the base64 encoded, serialized report to chrome://safe-browsing

To see the full report, base64 decode it and then parse as a
ClientSafeBrowsingReportRequest.

Bug:  767888 
Change-Id: I15856bb4d49b33059bf890324040146bc97b5d3e
Reviewed-on: https://chromium-review.googlesource.com/678253
Commit-Queue: Varun Khaneja <vakh@chromium.org>
Reviewed-by: Jialiu Lin <jialiul@chromium.org>
Reviewed-by: Luke Z <lpz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#503781}
[modify] https://crrev.com/a5f0c6cfea71ee9a8b8cfdd6b3d89d1b1bd3f980/components/safe_browsing/web_ui/safe_browsing_ui.cc

Initially landed in 63.0.3223.0

FMI: http://www.htmlgoodies.com/beyond/javascript/article.php/3458851

This is better: http://shortn/_Yoeb4Mj50n

Note that the string shown on chrome://safe-browsing is base64 url encoded.
The following function can be used to decode it in bash:

function base64_decode ()
{
  local input=$1
  input="$(echo $input | tr '-' '+')"
  input="$(echo $input | tr '_' '/')"
  echo $input | base64 --decode
}

lpz and I decided that it's better to use basic base64 encoding (non-URL).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bba0d6b9f4622ee7b127648b2cabc3dc22acb054

commit bba0d6b9f4622ee7b127648b2cabc3dc22acb054
Author: Varun Khaneja <vakh@chromium.org>
Date: Thu Sep 28 23:04:34 2017

Use basic base64 instead of URL encoded.

Bug:  767888 
Change-Id: Ib78c85028834b58510ad3f52189afcf0aa9fe30b
Reviewed-on: https://chromium-review.googlesource.com/691074
Reviewed-by: Luke Z <lpz@chromium.org>
Commit-Queue: Varun Khaneja <vakh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505203}
[modify] https://crrev.com/bba0d6b9f4622ee7b127648b2cabc3dc22acb054/components/safe_browsing/web_ui/safe_browsing_ui.cc