GitLab

What: Introduce the kFlocIdFinchConfigVersion feature param. On browser
start, invalidate floc and trigger an immediate recompute if the
version mismatches with the one when computing the last floc.

Why: This allows us to configure an immediate recompute when we feel
it's necessary.

How:
- Add the finch_config_version to FlocId, that allows it to be saved to
prefs at each computation along with other fields. On browser start,
check for version mismatch and handle it accordingly.
- In the InterestCohort string, this version replaces the position of
the previous constant kChromeFlocIdVersion. We expect most params to go
through finch in the near future so replacing the "chrome floc version"
part for now.
- Also move the compute_time to FlocId, as it's also logically fit
there, and we can keep the load/save function to one place.
- Move the floc features to //components as now the it's being checked
by the components.

Bug: 1159235
Change-Id: I0c80ed35ac5f181b18b860eb2f1a73acf6fd1432
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2595595Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Yao Xiao <yaoxia@chromium.org>
Cr-Commit-Position: refs/heads/master@{#838626}