i'm not seeing this behavior.  `sudo -v` never prompts.  the man page says it'll prompt if there is an entry for the user w/out NOPASSWD, but the only entry we install for the user is a NOPASSWD one:
/etc/sudoers/90_cros:vapier ALL=NOPASSWD: ALL

do you have any other entries or something ?  are you sure it's `sudo -v` *inside* the chroot and not *outside* ?

stimim and I both see this - "inside" chroot.

sudo -V
Sudo version 1.8.19p2
Sudoers policy plugin version 1.8.19p2
Sudoers file grammar version 45
Sudoers I/O plugin version 1.8.19p2

sudo -v

We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:

    #1) Respect the privacy of others.
    #2) Think before you type.
    #3) With great power comes great responsibility.

Password:

/etc/sudoers:

root ALL=(ALL) ALL

/etc/sudoers.d/90_cros:

Defaults env_keep += "CHROMEOS_OFFICIAL CHROMEOS_VERSION_AUSERVER CHROMEOS_VERSION_DEVSERVER CHROMEOS_VERSION_TRACK GCC_GITHASH GIT_AUTHOR_EMAIL GIT_AUTHOR_NAME GIT_COMMITTER_EMAIL GIT_COMMITTER_NAME GIT_PROXY_COMMAND GIT_SSH RSYNC_PROXY SSH_AGENT_PID SSH_AUTH_SOCK USE all_proxy ftp_proxy http_proxy https_proxy no_proxy CROS_WORKON_SRCROOT PORTAGE_USERNAME"
%adm ALL=(ALL) ALL
root ALL=(ALL) ALL
hungte ALL=NOPASSWD: ALL

/etc/sudoers.d/95_cros_base:

chronos ALL=(ALL) ALL

probably because my account is in adm group?

# groups
adm floppy audio cdrom video portage eng

Yes - after I've commented the %adm line, "sudo -v" won't complain for password.

Should we remove %adm, or ?

i can't find any history behind the adm entry.  it goes back to the original commits in 2009.  the group isn't used inside of the sdk either so shouldn't need to propagate it over.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/crosutils/+/57fce7bbf9839a8bd9fb4e4baa874c9c6b2ec87a

commit 57fce7bbf9839a8bd9fb4e4baa874c9c6b2ec87a
Author: Wei-Han Chen <stimim@google.com>
Date: Thu Sep 07 22:01:05 2017

chroot_version_hooks.d: make `sudo -v` don't ask for password

Even though we mark the user as NOPASSWD, if any other rules match
them, the `sudo -v` command ends up prompting for a password.  Add
a rule disabling that in case rules happen to trigger it.

BUG= chromium:762445 
TEST=cros_sdk --nousepkg --replace --enter --nouse-image; sudo -v

Change-Id: I3cb5abea515e8416431740d1bb4b4c6cfeb224cf
Reviewed-on: https://chromium-review.googlesource.com/652206
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>

[add] https://crrev.com/57fce7bbf9839a8bd9fb4e4baa874c9c6b2ec87a/chroot_version_hooks.d/152_rewrite_sudoers.d
[modify] https://crrev.com/57fce7bbf9839a8bd9fb4e4baa874c9c6b2ec87a/chroot_version_hooks.d/45_rewrite_sudoers.d