Sounds like we need to add to licences.py SPECIAL_CASES?

Steve, you set this up - can you take a look?

Actually, SPECIAL_CASES is just a replacement for README.chromium. It doesn't have a mechanism for omitting the URL.

In this case, there is no URL because third_party/metrics_proto is the canonical public repository for this code, since upstream is in an internal google3 repository. +dpranke to advise on how best to handle this.

maybe just add www.google.com and a comment?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a3db9c7163f755534cf980a81904bec6cef41175

commit a3db9c7163f755534cf980a81904bec6cef41175
Author: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Date: Tue Mar 13 22:07:48 2018

metrics_proto: Set URL and Short Name in README.chromium

The URL field is not optional in README.chromium, so //tools/licenses.py is
currently failing with

    licenses.LicenseError: couldn't find 'URL' line in README.chromium or licences.py SPECIAL_CASES

in //third_party/metrics_proto.

The actual development repository is not public, and the code in the
Chromium tree acts as the canonical public repository. Add an explanation
instead of a URL in a similar fashion to what is already done in:
* //third_party/bazel/desugar
* //third_party/gvr-android-keyboard
* //third_party/instrumented_libraries
* //third_party/s2cellid

While here, also set a Short Name; even though licenses.py does not
complain, README.chromium.template does not say it is an optional field.

Bug:  805849 
Change-Id: I1810e8523a2d3bd210855b2a7c1f997fdb0c7dda
Reviewed-on: https://chromium-review.googlesource.com/960028
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#542933}
[modify] https://crrev.com/a3db9c7163f755534cf980a81904bec6cef41175/third_party/metrics_proto/README.chromium