Introduce an admin policy to control 3DES

For now, the default is still that 3DES is enabled. The policy is
available one release early so administrators can test ahead of time. In
M93, we'll flip the default, at which point the policy will be a
temporary option for administrators who need more time. Finally, in M95,
we'll remove the option altogether.

I called the policy TripleDESEnabled to avoid mishaps with names
starting with digits (they're invalid variable names in C++). The cipher
is called, variously, "triple DES", "3DES", "TDES", and apparently
sometimes even "TDEA". 3DES is the usual spelling in TLS, but since it's
invalid, I've gone with spelled out "triple DES" spelling.

Given the low numbers (0.00%) and how long this algorithm has been
obsolete, we don't anticipate the removal to have much, if any, impact
and are providing the admin policy just in case.

Bug: 1203442
Change-Id: I1e7dd64f5398d258872012d8ed0d802786e1b6dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2860743
Commit-Queue: David Benjamin <davidben@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Emily Stark <estark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#879154}
NOKEYCHECK=True
GitOrigin-RevId: aabf91b764ebde6b8e3302563a71efc1c670e700
4 files changed