commit e5ec77c5c2a65b2cad01506faecd9bca61f1dbc4
author thefrog <thefrog@chromium.org> Thu Feb 02 01:09:00 2023
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Feb 02 01:09:00 2023
tree 15f7c92dd99a6cb212304139d3c337ce54ad2016
parent 89990a9ca8cb82e0eb990bca52900e1de2a705e1

Filter out experiment results that wouldn't warn user even if unsafe

Even if the threat type of a lookup response is unsafe, a warning may
still not be shown (e.g. prefetch, already bypassed site, etc.). For
these cases, we generally avoid including them in the logged results of
the experiment. When there are redirects, we still log results if some
but not all of them match this case, but we do so under a different
histogram prefix to allow segmenting.

Implementation details:
 - The code refers to this case as whether a check is "eligible".
 - SafeBrowsingLookupMechanismExperimenter will not complete the
experiment until it has received information for every CheckToRun about
its eligibility.
 - These checks are performed after the experiment completes but before
a warning is shown (if relevant). This is because 1) we still want the
experiment to run so that the different mechanisms can cache the results
for later reuse, and 2) one of the criteria (IsAllowlisted) can be
modified once the warning is shown, so we must check it before that.
 - Most of the ineligibility matching criteria must be performed on the
UI thread, whereas the experiment runs on the IO thread.
 - When there are redirects, it is possible for some of the requests to
be eligible while some are not. This can happen if one of the requests
is for a site that was already bypassed, or if the tab disappears
partway through the experiment but late enough that it doesn’t cancel
it. In these cases, we still log the experiment results. We also add a
log to track how often this is occurring, since we expect it is
infrequent.

Bug: 1392144

Change-Id: I9a52c54504adb5b4e4403ac4eae510f1d8781c16
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4195319
Commit-Queue: thefrog <thefrog@chromium.org>
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Reviewed-by: Xinghui Lu <xinghuilu@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Reviewed-by: Ali Juma <ajuma@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1100212}