I will work on the client code right now.

Upon further inspection, it appears we inherited this from CWS / extension updater.

I suggest we have the client transmit both attributes, then, and do a more gradual transition of the server side configs.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/704c72eefaae1677676c4d4e50311158a58f43a3

commit 704c72eefaae1677676c4d4e50311158a58f43a3
Author: Sorin Jianu <sorin@chromium.org>
Date: Mon Nov 19 23:24:53 2018

Component updater should use testsource=dev in addition to testrequest=1

With this change, the configurator code injects both values.

extra_info_["testrequest"] = "1";
extra_info_["testsource"] = "dev";

Bug: 906641
Change-Id: I4cd3f68b9b292f2d76b95d3678bd6df0cd437e73
Reviewed-on: https://chromium-review.googlesource.com/c/1343294
Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Commit-Queue: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609500}
[modify] https://crrev.com/704c72eefaae1677676c4d4e50311158a58f43a3/components/component_updater/configurator_impl.cc
[modify] https://crrev.com/704c72eefaae1677676c4d4e50311158a58f43a3/components/component_updater/configurator_impl_unittest.cc

This issue has an owner, a component and a priority, but is still listed as untriaged or unconfirmed. By definition, this bug is triaged. Changing status to "assigned". Please reach out to me if you disagree with how I've done this.