I wonder if this could be covered by logging the whole request -- see  crbug.com/668216 

I guess we care about the experiments exposed through headers most and having the whole request would help with a lot of things.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/429f312b0855e94bd2facaa27842513fc2c362dd

commit 429f312b0855e94bd2facaa27842513fc2c362dd
Author: sfiera <sfiera@chromium.org>
Date: Mon Apr 24 16:17:57 2017

List our features in ntp_snippets::kAllFeatures

Move the notifications feature into the component for consistency, even
though nothing in the component actually uses it.

Having this list lets us answer questions list "what active experiment
IDs correspond to our features?" Active experiments are important for
debugging, but they're only loosely tied to features.

BUG= 713038 

Review-Url: https://codereview.chromium.org/2831553003
Cr-Commit-Position: refs/heads/master@{#466640}

[modify] https://crrev.com/429f312b0855e94bd2facaa27842513fc2c362dd/chrome/browser/BUILD.gn
[modify] https://crrev.com/429f312b0855e94bd2facaa27842513fc2c362dd/chrome/browser/about_flags.cc
[modify] https://crrev.com/429f312b0855e94bd2facaa27842513fc2c362dd/chrome/browser/android/chrome_feature_list.cc
[modify] https://crrev.com/429f312b0855e94bd2facaa27842513fc2c362dd/chrome/browser/android/ntp/content_suggestions_notification_helper.cc
[modify] https://crrev.com/429f312b0855e94bd2facaa27842513fc2c362dd/chrome/browser/android/ntp/content_suggestions_notifier_service.cc
[modify] https://crrev.com/429f312b0855e94bd2facaa27842513fc2c362dd/chrome/browser/ntp_snippets/content_suggestions_notifier_service_factory.cc
[delete] https://crrev.com/e1efe87a94f1aaf93e461b52ed395b3e3e75ed68/chrome/browser/ntp_snippets/ntp_snippets_features.cc
[delete] https://crrev.com/e1efe87a94f1aaf93e461b52ed395b3e3e75ed68/chrome/browser/ntp_snippets/ntp_snippets_features.h
[modify] https://crrev.com/429f312b0855e94bd2facaa27842513fc2c362dd/components/ntp_snippets/features.cc
[modify] https://crrev.com/429f312b0855e94bd2facaa27842513fc2c362dd/components/ntp_snippets/features.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9a5bc285254c5d9cbf47ea862a64324804044be1

commit 9a5bc285254c5d9cbf47ea862a64324804044be1
Author: sfiera <sfiera@chromium.org>
Date: Mon Apr 24 18:27:29 2017

List relevant IDs from Finch in snippets-internals

"Relevant" IDs are ones that are associated with our features. This will
help us investigate quality issues on the server when we want to know
what configuration a user is using.

No explanation is given for the meaning of the IDs; we don't have that
for most of them in Chrome, nor I believe do we want to add it.

Note that this excludes variation IDs set from the command line with
--force-variation-ids; it's impossible to know with Chrome if those are
our IDs or someone else's (and showing them is mostly not important to
the debugging use case anyway). It also excludes variation IDs set from
chrome://flags, which I'm investigating.

BUG= 713038 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2826013002
Cr-Commit-Position: refs/heads/master@{#466694}

[modify] https://crrev.com/9a5bc285254c5d9cbf47ea862a64324804044be1/chrome/browser/resources/snippets_internals.html
[modify] https://crrev.com/9a5bc285254c5d9cbf47ea862a64324804044be1/chrome/browser/ui/webui/snippets_internals_message_handler.cc