Let's keep the opacity change separate. I'll just work on delaying the animation and creation of backdrop.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/014337427a650172113ddc73b3c49a8604b26b47

commit 014337427a650172113ddc73b3c49a8604b26b47
Author: Mitsuru Oshima <oshima@chromium.org>
Date: Tue Nov 06 02:46:01 2018

Show ItemWidget/Backdrop after overview animation ends.

Bug:  901402 
Test: manual. The window title fades in after overview
  animation ends (in clamshell, tablet, from home launcher).
  and hides immediately when exiting.

Change-Id: I06b25ebea428439ec6e7ab2751db74409971855f
Reviewed-on: https://chromium-review.googlesource.com/c/1316363
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605578}
[modify] https://crrev.com/014337427a650172113ddc73b3c49a8604b26b47/ash/wm/overview/scoped_transform_overview_window.cc
[modify] https://crrev.com/014337427a650172113ddc73b3c49a8604b26b47/ash/wm/overview/scoped_transform_overview_window.h
[modify] https://crrev.com/014337427a650172113ddc73b3c49a8604b26b47/ash/wm/overview/window_grid.cc
[modify] https://crrev.com/014337427a650172113ddc73b3c49a8604b26b47/ash/wm/overview/window_selector.cc
[modify] https://crrev.com/014337427a650172113ddc73b3c49a8604b26b47/ash/wm/overview/window_selector_item.cc
[modify] https://crrev.com/014337427a650172113ddc73b3c49a8604b26b47/ash/wm/overview/window_selector_item.h

This is one of performance turning work required for m71.
Chrome wasn't upreved yesterday, so I tested the following scenario in today's ToT.

* enter/exit overview in clamshell.
* enter/exit overview in tablet mode
* enter/exit overview in split screen
* enter/exit overview from tablet  home screeen.

Approved for M71 ChromeOS

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6ff29915e8cb3bed227589df721dc26b372bb3cb

commit 6ff29915e8cb3bed227589df721dc26b372bb3cb
Author: Mitsuru Oshima <oshima@chromium.org>
Date: Wed Nov 07 00:46:37 2018

Show ItemWidget/Backdrop after overview animation ends.

Bug:  901402 
Test: manual. The window title fades in after overview
  animation ends (in clamshell, tablet, from home launcher).
  and hides immediately when exiting.

(cherry picked from commit 014337427a650172113ddc73b3c49a8604b26b47)

Reviewed-on: https://chromium-review.googlesource.com/c/1316363
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#605578}
Change-Id: I61d58eec1e2f09e80f506012957b95cec66ee3d9
Reviewed-on: https://chromium-review.googlesource.com/c/1321792
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/branch-heads/3578@{#553}
Cr-Branched-From: 4226ddf99103e493d7afb23a4c7902ee496108b6-refs/heads/master@{#599034}
[modify] https://crrev.com/6ff29915e8cb3bed227589df721dc26b372bb3cb/ash/wm/overview/scoped_transform_overview_window.cc
[modify] https://crrev.com/6ff29915e8cb3bed227589df721dc26b372bb3cb/ash/wm/overview/scoped_transform_overview_window.h
[modify] https://crrev.com/6ff29915e8cb3bed227589df721dc26b372bb3cb/ash/wm/overview/window_grid.cc
[modify] https://crrev.com/6ff29915e8cb3bed227589df721dc26b372bb3cb/ash/wm/overview/window_selector.cc
[modify] https://crrev.com/6ff29915e8cb3bed227589df721dc26b372bb3cb/ash/wm/overview/window_selector_item.cc
[modify] https://crrev.com/6ff29915e8cb3bed227589df721dc26b372bb3cb/ash/wm/overview/window_selector_item.h

The following revision refers to this bug: 
https://chromium.googlesource.com/chromium/src.git/+/6ff29915e8cb3bed227589df721dc26b372bb3cb

Commit: 6ff29915e8cb3bed227589df721dc26b372bb3cb
Author: oshima@chromium.org
Commiter: oshima@chromium.org
Date: 2018-11-07 00:46:37 +0000 UTC

Show ItemWidget/Backdrop after overview animation ends.

Bug:  901402 
Test: manual. The window title fades in after overview
  animation ends (in clamshell, tablet, from home launcher).
  and hides immediately when exiting.

(cherry picked from commit 014337427a650172113ddc73b3c49a8604b26b47)

Reviewed-on: https://chromium-review.googlesource.com/c/1316363
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#605578}
Change-Id: I61d58eec1e2f09e80f506012957b95cec66ee3d9
Reviewed-on: https://chromium-review.googlesource.com/c/1321792
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/branch-heads/3578@{#553}
Cr-Branched-From: 4226ddf99103e493d7afb23a4c7902ee496108b6-refs/heads/master@{#599034}