Add a SecureDnsPolicy to the request parameters

This change replaces
net::HostManager::ResolveHostParameters::secure_dns_mode_override
with a SecureDnsPolicy.  This makes the purpose of this field
more explicit, avoids supporting the expression of policy combinations
that are not actually used, and provides a means to support new policies
that are not simply overriding the Secure DNS mode.

Blocked by Id8f3eb7e9ddefc6d35241c8843d131f79ed445ac

Bug: 1200908
Change-Id: I40f344f5972f2cb21a1196b5879475659ba2f840
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2869030
Reviewed-by: Eric Orth <ericorth@chromium.org>
Commit-Queue: Eric Orth <ericorth@chromium.org>
Auto-Submit: Ben Schwartz <bemasc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#879573}
NOKEYCHECK=True
GitOrigin-RevId: 432ce031473f43a28a1e36a04d4b46f993086e1c
18 files changed