+tbarzic, is it the same with the issue you worked on? I believe this is related to power_event_observer?

I've had a cl in plan that should address this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c7dbb870ac431aa1767e2e0c9a68106502f0571e

commit c7dbb870ac431aa1767e2e0c9a68106502f0571e
Author: Toni Barzic <tbarzic@chromium.org>
Date: Tue Mar 13 23:08:10 2018

Wait for animated wallpaper changes to finish before suspending displays

PowerEventObserver delays display suspend until lock screen UI is shown
and compositors submit enough frames to know the UI changes have reached
displays.
This does not account for wallpaper changes due to screen lock:
  * On screen lock, the active wallpaper will be changed with its blurred
    version.
  * If screen lock changes the active user (e.g. if the screen is locked
    from the secondary user), the wallpaper will change to the new
    active user's blurred wallpaper.
Given that PowerEventObserver does not ensure wallpaper switch is done
before it stops drawing to the display, the first frame shown on the
device resume might still contain the UI from before wallpaper change.

This changes PowerEventObserver to additionally wait for any active
wallpaper changes (which can be detected by checking
WallpaperWidgetController::IsAnimating - set while wallpaper widget is
being changed) to finish before it starts waiting for compositor frames
to get composited, thus ensuring the correct wallpaper is set when the
display/compositing is suspended.

Adds the following methods to WallpaperWidgetController:
  * AddPendingAnimationEndCallback - to provide a way for
    PowerEventObserver to get notified when the pending wallpaper change
    completes
  * EndPendingAnimation which can be used to force immediate wallpaper
    change when device starts suspending (and prevents suspend flow from
    being blocked on unnecessarily waiting for new wallpaper animation)

BUG= 820436 , 803762 

Change-Id: Iad2074280ebba740b95c50b9d60a028bf5a0d45c
Reviewed-on: https://chromium-review.googlesource.com/956757
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Wenzhao (Colin) Zang <wzang@chromium.org>
Commit-Queue: Toni Barzic <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542945}
[modify] https://crrev.com/c7dbb870ac431aa1767e2e0c9a68106502f0571e/ash/system/power/power_event_observer.cc
[modify] https://crrev.com/c7dbb870ac431aa1767e2e0c9a68106502f0571e/ash/system/power/power_event_observer.h
[modify] https://crrev.com/c7dbb870ac431aa1767e2e0c9a68106502f0571e/ash/system/power/power_event_observer_unittest.cc
[modify] https://crrev.com/c7dbb870ac431aa1767e2e0c9a68106502f0571e/ash/wallpaper/wallpaper_widget_controller.cc
[modify] https://crrev.com/c7dbb870ac431aa1767e2e0c9a68106502f0571e/ash/wallpaper/wallpaper_widget_controller.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/524c3741778d2b9e77645de1605711efa68896b2

commit 524c3741778d2b9e77645de1605711efa68896b2
Author: Toni Barzic <tbarzic@chromium.org>
Date: Fri Mar 23 21:02:32 2018

Merge: Wait for animated wallpaper changes to finish before suspending displays

PowerEventObserver delays display suspend until lock screen UI is shown
and compositors submit enough frames to know the UI changes have reached
displays.
This does not account for wallpaper changes due to screen lock:
  * On screen lock, the active wallpaper will be changed with its blurred
    version.
  * If screen lock changes the active user (e.g. if the screen is locked
    from the secondary user), the wallpaper will change to the new
    active user's blurred wallpaper.
Given that PowerEventObserver does not ensure wallpaper switch is done
before it stops drawing to the display, the first frame shown on the
device resume might still contain the UI from before wallpaper change.

This changes PowerEventObserver to additionally wait for any active
wallpaper changes (which can be detected by checking
WallpaperWidgetController::IsAnimating - set while wallpaper widget is
being changed) to finish before it starts waiting for compositor frames
to get composited, thus ensuring the correct wallpaper is set when the
display/compositing is suspended.

Adds the following methods to WallpaperWidgetController:
  * AddPendingAnimationEndCallback - to provide a way for
    PowerEventObserver to get notified when the pending wallpaper change
    completes
  * EndPendingAnimation which can be used to force immediate wallpaper
    change when device starts suspending (and prevents suspend flow from
    being blocked on unnecessarily waiting for new wallpaper animation)

BUG= 820436 , 803762 
TBR=tbarzic@chromium.org

(cherry picked from commit c7dbb870ac431aa1767e2e0c9a68106502f0571e)

Change-Id: Iad2074280ebba740b95c50b9d60a028bf5a0d45c
Reviewed-on: https://chromium-review.googlesource.com/956757
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Wenzhao (Colin) Zang <wzang@chromium.org>
Commit-Queue: Toni Barzic <tbarzic@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#542945}
Reviewed-on: https://chromium-review.googlesource.com/978842
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Cr-Commit-Position: refs/branch-heads/3359@{#408}
Cr-Branched-From: 66afc5e5d10127546cc4b98b9117aff588b5e66b-refs/heads/master@{#540276}
[modify] https://crrev.com/524c3741778d2b9e77645de1605711efa68896b2/ash/system/power/power_event_observer.cc
[modify] https://crrev.com/524c3741778d2b9e77645de1605711efa68896b2/ash/system/power/power_event_observer.h
[modify] https://crrev.com/524c3741778d2b9e77645de1605711efa68896b2/ash/system/power/power_event_observer_unittest.cc
[modify] https://crrev.com/524c3741778d2b9e77645de1605711efa68896b2/ash/wallpaper/wallpaper_widget_controller.cc
[modify] https://crrev.com/524c3741778d2b9e77645de1605711efa68896b2/ash/wallpaper/wallpaper_widget_controller.h