commit 533ae3d7705c36be9f0a237e8d0d111f09ec59df
author Alex Turner <alexmt@chromium.org> Tue Feb 02 19:44:06 2021
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue Feb 02 19:44:06 2021
tree a4deb3f37129ff9fd622eb66940e677dad86fa06
parent 98dc1750c10bb56376b90a6c632bffc6cbb89b73

Track the evidence that determines whether a subframe is tagged as an ad

Subframes are currently considered as ad frames once any of the
following criteria are met:
 - the parent frame is an ad frame
 - ad script was on the v8 stack when the frame was created, or
 - the URL is considered an ad by the filter list
Whenever one of these criteria is triggered, the frame is immediately
tagged.

Once a frame is tagged, no record is kept of which criteria were the
cause. Additionally, the current system does not allow for more complex
decision conditions, which are necessary to avoid certain known false
positives. In particular, we aim to supporting ignoring the second
criterion above (ad script being on the stack at frame creation) if
either the URL matches an allowlist rule or the URL has the same eTLD+1
as the main frame. (See the design doc linked in the bug.)

To rectify the first problem, we maintain a SubframeAdEvidence object in
the browser for each subframe. This object tracks whether each criterion
has been triggered. Once a frame is tagged as an ad, this object is
frozen to reflect the cause(s).

This cl is preliminary: it does not affect ad tagging and the new
evidence object is not yet used; however, it enables two follow-up cls.
The first follow-up will transition subframe ad tagging to use the
evidence object. The second will modify the decision condition to avoid
known false positives, as described above.

Bug: 1101584
Change-Id: Ia20bdbd348924665e6ccc940e3a97a7a3a414d7e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2419372
Commit-Queue: Alex Turner <alexmt@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Reviewed-by: Chris Palmer <palmer@chromium.org>
Reviewed-by: John Delaney <johnidel@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#849715}