I think this feature is corresponding to this spec: 
https://screenshot.googleplex.com/Stf7U5FGsgB

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/886245aa6e6e03f70a26bc4cc1bbbf0b6d54fe4d

commit 886245aa6e6e03f70a26bc4cc1bbbf0b6d54fe4d
Author: Weidong Guo <weidongg@chromium.org>
Date: Tue Jul 18 17:58:59 2017

Make StartPageView vertically centered

Changes:
1. Make StartPageView vertically centered in fullscreen mode.

specs: https://screenshot.googleplex.com/Stf7U5FGsgB

BUG= 735487 

Change-Id: I9795e23e73d8cd28acb6217584fc08c0bc8e0f3c
Reviewed-on: https://chromium-review.googlesource.com/575665
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487522}
[modify] https://crrev.com/886245aa6e6e03f70a26bc4cc1bbbf0b6d54fe4d/ui/app_list/views/search_result_page_view.cc
[modify] https://crrev.com/886245aa6e6e03f70a26bc4cc1bbbf0b6d54fe4d/ui/app_list/views/start_page_view.cc
[modify] https://crrev.com/886245aa6e6e03f70a26bc4cc1bbbf0b6d54fe4d/ui/app_list/views/start_page_view.h

This is not WAI for portrait tablet mode.

Looks like we don't have this spec: https://screenshot.googleplex.com/Stf7U5FGsgB

When I hit ESC in fullscreen all apps mode, it does not get into what shown in the spec.

And from this spec: https://screenshot.googleplex.com/gitzBzANKYg, it seems we don't need to vertically center AppsContainerView as well.

Coming back to this with proper spec, sorry about that.
You can find the updated spec for the vertical alignment behavior here:
https://gallery.googleplex.com/projects/MCHbtQVoQ2HCZY5BZ8F2qhKy/files/MCGAAf1s-t7xY9qCCrLpNXqWwMSJbxAVNpw

Excerpt also attached.
We need to center the all apps as well as the search box in the center of the screen at the condition of always leaving 24px top padding minimum between search box and the top edge of the screen.

Let me know if you have any question.

Deleted: excerpt.png 215 KB

	excerpt.png 215 KB View Download

Here's the updated spec following our peeking/fullscreen removal of "suggested apps" label.

- height of all app scroll area is now 623px instead of 633px
- Top and bottom fade-out areas are now 24px instead of 21px.

Specs available here:
https://gallery.googleplex.com/projects/MCHbtQVoQ2HCZY5BZ8F2qhKy/files/MCH5f23P589MDjjCu48OZYJ3wMSJbxAVNpw

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/48052e3a9007a8068978b416110f94de1b49cb8a

commit 48052e3a9007a8068978b416110f94de1b49cb8a
Author: Weidong Guo <weidongg@chromium.org>
Date: Tue Aug 08 00:19:39 2017

Make App List Grid vertically centered

Changes:
1. Make the AppsContainerView vertically centered in screen.
2. Enlarge the ContentsView according to the height of display to
accommodate AppsContainerView.

Screenshot: https://screenshot.googleplex.com/w7sT5CSCeWE

BUG= 735487 

Change-Id: I34d263d30b26d990f104224c10deeefa04c4c874
Reviewed-on: https://chromium-review.googlesource.com/602876
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Yury Khmel <khmel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#492465}
[modify] https://crrev.com/48052e3a9007a8068978b416110f94de1b49cb8a/ui/app_list/views/apps_container_view.cc
[modify] https://crrev.com/48052e3a9007a8068978b416110f94de1b49cb8a/ui/app_list/views/apps_container_view.h
[modify] https://crrev.com/48052e3a9007a8068978b416110f94de1b49cb8a/ui/app_list/views/contents_view.cc
[modify] https://crrev.com/48052e3a9007a8068978b416110f94de1b49cb8a/ui/app_list/views/contents_view.h

We probably should center Y in available work area, not display area. With bottom shelf aligned, fullscreen app list seems too close to shelf.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2e72b474826fcc273d9ce3315c7eebb3f1a3804f

commit 2e72b474826fcc273d9ce3315c7eebb3f1a3804f
Author: Weidong Guo <weidongg@chromium.org>
Date: Wed Aug 09 21:48:50 2017

Make Apps List Grid vertically centered in work area

Changes:
Make AppsContainerView vertically centered in screen's work area which
does not include the area of shelf.

BUG= 735487 

Change-Id: I5efd06884bf395a4218dd3eca49cca562bd9daec
Reviewed-on: https://chromium-review.googlesource.com/609031
Reviewed-by: Yury Khmel <khmel@chromium.org>
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#493154}
[modify] https://crrev.com/2e72b474826fcc273d9ce3315c7eebb3f1a3804f/ui/app_list/views/contents_view.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/907dcc713dd69372813f468922c10db983c768c6

commit 907dcc713dd69372813f468922c10db983c768c6
Author: Maajid <maajid@chromium.org>
Date: Thu Aug 10 20:51:26 2017

Make App List Grid vertically centered

Changes:
1. Make the AppsContainerView vertically centered in screen.
2. Enlarge the ContentsView according to the height of display to
accommodate AppsContainerView.

Screenshot: https://screenshot.googleplex.com/w7sT5CSCeWE

BUG= 735487 
TBR=weidongg@chromium.org

(cherry picked from commit 48052e3a9007a8068978b416110f94de1b49cb8a)

Change-Id: I34d263d30b26d990f104224c10deeefa04c4c874
Reviewed-on: https://chromium-review.googlesource.com/602876
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Yury Khmel <khmel@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#492465}
Reviewed-on: https://chromium-review.googlesource.com/611125
Reviewed-by: Vadim Tryshev <vadimt@chromium.org>
Cr-Commit-Position: refs/branch-heads/3163@{#460}
Cr-Branched-From: ff259bab28b35d242e10186cd63af7ed404fae0d-refs/heads/master@{#488528}
[modify] https://crrev.com/907dcc713dd69372813f468922c10db983c768c6/ui/app_list/views/apps_container_view.cc
[modify] https://crrev.com/907dcc713dd69372813f468922c10db983c768c6/ui/app_list/views/apps_container_view.h
[modify] https://crrev.com/907dcc713dd69372813f468922c10db983c768c6/ui/app_list/views/contents_view.cc
[modify] https://crrev.com/907dcc713dd69372813f468922c10db983c768c6/ui/app_list/views/contents_view.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4bf680ae4e878b7123dc986b7392c889de428bf9

commit 4bf680ae4e878b7123dc986b7392c889de428bf9
Author: Maajid <maajid@chromium.org>
Date: Thu Aug 10 23:55:02 2017

Make Apps List Grid vertically centered in work area

Changes:
Make AppsContainerView vertically centered in screen's work area which
does not include the area of shelf.

BUG= 735487 
TBR=weidongg@chromium.org

(cherry picked from commit 2e72b474826fcc273d9ce3315c7eebb3f1a3804f)

Change-Id: I5efd06884bf395a4218dd3eca49cca562bd9daec
Reviewed-on: https://chromium-review.googlesource.com/609031
Reviewed-by: Yury Khmel <khmel@chromium.org>
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#493154}
Reviewed-on: https://chromium-review.googlesource.com/611288
Reviewed-by: Vadim Tryshev <vadimt@chromium.org>
Cr-Commit-Position: refs/branch-heads/3163@{#477}
Cr-Branched-From: ff259bab28b35d242e10186cd63af7ed404fae0d-refs/heads/master@{#488528}
[modify] https://crrev.com/4bf680ae4e878b7123dc986b7392c889de428bf9/ui/app_list/views/contents_view.cc