I don't have many opinions about this. Right now, when I hold the lock key on a caroline device, the shelf and status area are animated: the shelf icons fade out, the status icons change, the shelf turns black, and the "Shut down" and "Sign out" button slide in from the left. Is it possible to make all of those changes happen immediately instead of animating them when the side power button is tapped?

shelf fade out -> shelf immediately hide, should be addressed in: https://chromium-review.googlesource.com/c/chromium/src/+/644230

status area: for tot Chrome, it will change from back to semi-transparent. I need UI/UX suggestions whether we need to hide it first and then show it when lock screen/overlay shows.

shelf turns black: for new lock screen, shelf will not turn black

"shut down" and "sign out" animation -> make it appear instantly. I need to consult jdufault@ or wzang@.

I could remove the animation of 'shut down' and 'sign out', but they still may not show instantly as they are implemented in Web UI and there's delay in loading them. But I'm working on re-implementing them using views-based UI (targeted at M63) and I will disable the animation in this case. 

Actually I had a WIP CL that adds a 'FADE IN' animation to SessionStateAnimator::LAUNCHER (renamed as SHELF) in |StartPostLockAnimation()|, because the shelf fades out previously and we need to it show again (the app list buttons are replaced with the sign out button etc.). However this issue suggests that we should distinguish between a regular lock action and a lock made by the power button, and show the shelf immediately in the latter case. Is it possible to distinguish the two cases in |StartPostLockAnimation()|?

Yes, there is an  issue 748732  tracking no animation for post lock animation, which I will do in these days.
Thanks for the info. So there will be shelf animation added in StartPostLockAnimation. I think I or either you can make it no animation when 748732 is done.

For 'shut down' and 'sign out' animations, if they could be removed for the cases described in 748732 only, that would be good!

OK, I will remember to disable the animation for 'shutdown' button in the case of  issue 748732  only. I think it will be easy to do after  issue 748732  is fixed.

My CL to bind wallpaper reparent with session state might make this issue more obvious because it takes a while to get to LOCKED session state. I wonder whether we should introduce a LOCKING state that sets immediately when we start to lock and move wallpaper on that state.

I think views-based shelf will make this easier, since it should be able to build the new UI and display it in under a single frame.

It is not worth the effort to do this for the webui lock screen.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1250f2be8fc80668ed12604fb86d5a1ac3818a24

commit 1250f2be8fc80668ed12604fb86d5a1ac3818a24
Author: Qiang Xu <warx@chromium.org>
Date: Thu Aug 31 18:01:00 2017

cros: immediately hide Shelf Container for screen off locking animation

changes:
- Rename SessionStateAnimator::LAUNCHER to SessionStateAnimator::SHELF,
to match the exact container name: kShellWindowId_ShelfContainer.
- Hiding shelf container in addition to non lock screen containers.
- Send EVENT_LOCK_ANIMATION_STARTED for LockWithoutAnimation() in hope
of the observation on this event doesn't break.

Bug:  760775 
Test: coverted by tests. Also tested on device.
Change-Id: I304d954ccb2510f8136268ffcb1297025e8be738
Reviewed-on: https://chromium-review.googlesource.com/644230
Reviewed-by: Dan Erat (OOO Fri-Mon) <derat@chromium.org>
Commit-Queue: Qiang(Joe) Xu <warx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#498919}
[modify] https://crrev.com/1250f2be8fc80668ed12604fb86d5a1ac3818a24/ash/system/power/power_event_observer_unittest.cc
[modify] https://crrev.com/1250f2be8fc80668ed12604fb86d5a1ac3818a24/ash/system/power/tablet_power_button_controller_unittest.cc
[modify] https://crrev.com/1250f2be8fc80668ed12604fb86d5a1ac3818a24/ash/wm/lock_state_controller.cc
[modify] https://crrev.com/1250f2be8fc80668ed12604fb86d5a1ac3818a24/ash/wm/lock_state_controller.h
[modify] https://crrev.com/1250f2be8fc80668ed12604fb86d5a1ac3818a24/ash/wm/lock_state_controller_unittest.cc
[modify] https://crrev.com/1250f2be8fc80668ed12604fb86d5a1ac3818a24/ash/wm/session_state_animator.cc
[modify] https://crrev.com/1250f2be8fc80668ed12604fb86d5a1ac3818a24/ash/wm/session_state_animator.h
[modify] https://crrev.com/1250f2be8fc80668ed12604fb86d5a1ac3818a24/ash/wm/session_state_animator_impl.cc
[modify] https://crrev.com/1250f2be8fc80668ed12604fb86d5a1ac3818a24/ash/wm/session_state_animator_impl_unittest.cc
[modify] https://crrev.com/1250f2be8fc80668ed12604fb86d5a1ac3818a24/ash/wm/test_session_state_animator.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/dfe6d1724c3ab0dd43fba6bdea338284eca9f474

commit dfe6d1724c3ab0dd43fba6bdea338284eca9f474
Author: Qiang Xu <warx@chromium.org>
Date: Wed Sep 13 21:33:14 2017

m61 merge: cros: immediately hide Shelf Container for screen off locking animation

changes:
- Rename SessionStateAnimator::LAUNCHER to SessionStateAnimator::SHELF,
to match the exact container name: kShellWindowId_ShelfContainer.
- Hiding shelf container in addition to non lock screen containers.
- Send EVENT_LOCK_ANIMATION_STARTED for LockWithoutAnimation() in hope
of the observation on this event doesn't break.

TBR: derat@chromium.org

(cherry picked from commit 1250f2be8fc80668ed12604fb86d5a1ac3818a24)

Bug:  760775 
Test: coverted by tests. Also tested on device.
Change-Id: I304d954ccb2510f8136268ffcb1297025e8be738
Reviewed-on: https://chromium-review.googlesource.com/644230
Reviewed-by: Dan Erat (OOO Fri-Mon) <derat@chromium.org>
Commit-Queue: Qiang(Joe) Xu <warx@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#498919}
Reviewed-on: https://chromium-review.googlesource.com/665826
Reviewed-by: Qiang(Joe) Xu <warx@chromium.org>
Cr-Commit-Position: refs/branch-heads/3163@{#1191}
Cr-Branched-From: ff259bab28b35d242e10186cd63af7ed404fae0d-refs/heads/master@{#488528}
[modify] https://crrev.com/dfe6d1724c3ab0dd43fba6bdea338284eca9f474/ash/system/power/power_event_observer_unittest.cc
[modify] https://crrev.com/dfe6d1724c3ab0dd43fba6bdea338284eca9f474/ash/system/power/tablet_power_button_controller_unittest.cc
[modify] https://crrev.com/dfe6d1724c3ab0dd43fba6bdea338284eca9f474/ash/wm/lock_state_controller.cc
[modify] https://crrev.com/dfe6d1724c3ab0dd43fba6bdea338284eca9f474/ash/wm/lock_state_controller.h
[modify] https://crrev.com/dfe6d1724c3ab0dd43fba6bdea338284eca9f474/ash/wm/lock_state_controller_unittest.cc
[modify] https://crrev.com/dfe6d1724c3ab0dd43fba6bdea338284eca9f474/ash/wm/session_state_animator.cc
[modify] https://crrev.com/dfe6d1724c3ab0dd43fba6bdea338284eca9f474/ash/wm/session_state_animator.h
[modify] https://crrev.com/dfe6d1724c3ab0dd43fba6bdea338284eca9f474/ash/wm/session_state_animator_impl.cc
[modify] https://crrev.com/dfe6d1724c3ab0dd43fba6bdea338284eca9f474/ash/wm/session_state_animator_impl_unittest.cc
[modify] https://crrev.com/dfe6d1724c3ab0dd43fba6bdea338284eca9f474/ash/wm/test_session_state_animator.cc

delegate to wzang@ for views-based lock screen update and 'shutdown' button, etc.

There is a variable |post_lock_immediate_animation_| in LockStateController to indicate whether lock animation should be immediate.

Sure. I have a WIP CL checking that variable. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4ca20523c37be2604719682cc7c9265cffbd184d

commit 4ca20523c37be2604719682cc7c9265cffbd184d
Author: Wenzhao Zang <wzang@chromium.org>
Date: Wed Sep 20 00:42:32 2017

Add fade-in animation to make shelf visible on lock screen

The views-based shelf is hidden behind flag. The fade-in animation
is a no-op if the flag is not added because the shelf is in
non_lock_screen_containers without the flag. (Follow-up to CL 583942.)

Bug:  701157 ,  760775 
Change-Id: I14421b22c21361a7ff97e9c0e50a23ff0dd6fa45
Reviewed-on: https://chromium-review.googlesource.com/662417
Commit-Queue: Wenzhao (Colin) Zang <wzang@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Cr-Commit-Position: refs/heads/master@{#503008}
[modify] https://crrev.com/4ca20523c37be2604719682cc7c9265cffbd184d/ash/shelf/shelf_background_animator.cc
[modify] https://crrev.com/4ca20523c37be2604719682cc7c9265cffbd184d/ash/shelf/shelf_background_animator.h
[modify] https://crrev.com/4ca20523c37be2604719682cc7c9265cffbd184d/ash/system/power/power_event_observer_unittest.cc
[modify] https://crrev.com/4ca20523c37be2604719682cc7c9265cffbd184d/ash/system/power/tablet_power_button_controller_unittest.cc
[modify] https://crrev.com/4ca20523c37be2604719682cc7c9265cffbd184d/ash/wm/lock_state_controller.cc
[modify] https://crrev.com/4ca20523c37be2604719682cc7c9265cffbd184d/ash/wm/lock_state_controller_unittest.cc

Marked fix since the views-based lock screen and shelf are enabled by default.