The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/db81c0d222010b22a37695e6e42475e023e5d9db

commit db81c0d222010b22a37695e6e42475e023e5d9db
Author: Mark Cogan <marq@google.com>
Date: Thu Mar 22 13:21:13 2018

[iOS] Refactor tab grid transition animation (initial steps).

This CL refactors the tab grid transition animation by separating the
transition animator-specific logic (including getting state information
vie the transition state provider) from the animation itself.

The new GridTransitionAnimator object is a UIView sublcass that hosts
the proxy cell views used for the animation. It isn't dependent on the
specific view setup or timing of a transition animator, and so could
be used anywhere.

The transition animator still handles fading out the tab view (the BVC).
A future CL may move this logic into the BVC's -viewWillDisappear:.

This is a preparatory step to making the animator such that the reverse
animation can use it as well.

Bug:  804539 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I69382950f1fcc7b62f0afe365b1f1d85293d8f25
Reviewed-on: https://chromium-review.googlesource.com/973612
Commit-Queue: Mark Cogan <marq@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545055}
[modify] https://crrev.com/db81c0d222010b22a37695e6e42475e023e5d9db/ios/chrome/browser/ui/tab_grid/transitions/BUILD.gn
[add] https://crrev.com/db81c0d222010b22a37695e6e42475e023e5d9db/ios/chrome/browser/ui/tab_grid/transitions/grid_transition_animation.h
[add] https://crrev.com/db81c0d222010b22a37695e6e42475e023e5d9db/ios/chrome/browser/ui/tab_grid/transitions/grid_transition_animation.mm
[modify] https://crrev.com/db81c0d222010b22a37695e6e42475e023e5d9db/ios/chrome/browser/ui/tab_grid/transitions/tab_to_grid_animator.mm

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9427879ef09ad346dbb7b4ecf174e2411a1c152f

commit 9427879ef09ad346dbb7b4ecf174e2411a1c152f
Author: Mark Cogan <marq@google.com>
Date: Thu Mar 22 15:47:09 2018

[iOS] Further refactor tab grid transition animation.

This CL further refactors the grid animation in preparation for
supporting a reversable version. Each of the four primary steps in the
animation (positioning and scaling the selected and unselected cells in
both the regular and expanded positions) is extracted into a separate
method, and common code in those methods is further extracted to reduce
repitition.

Bug:  804539 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Ibabd01e9f01fb58198bcd14f39536a77dcdf2c39
Reviewed-on: https://chromium-review.googlesource.com/975462
Commit-Queue: Mark Cogan <marq@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545088}
[modify] https://crrev.com/9427879ef09ad346dbb7b4ecf174e2411a1c152f/ios/chrome/browser/ui/tab_grid/transitions/grid_transition_animation.mm

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/43c79ea79708e960b6bd859c2b6765e63052fcbc

commit 43c79ea79708e960b6bd859c2b6765e63052fcbc
Author: Mark Cogan <marq@google.com>
Date: Fri Mar 23 17:23:40 2018

[iOS] Grid-to-tab transition animation (still rough).

This CL is an initial implementation of the grid-to-tab animation.

GridTransitionAnimation now supports animations in both directions.
The reverse (grid-to-tab) animation is implemented similarly to the
tab-to-grid animation, with different relative timing for the various
stages, and starting with the cells in the regular positions and
animating to the expanded position.

GridToVisibleTabAnimator likewise is structured similarly to its
opposite, and the disappearing transitions in TabGridViewController
also mirror their appearing counterparts.

This produces a lot of near-duplicate code. Follow-up CLs will
refactor this into a cleaner structure.

The animation itself also needs improvement, particularly the
interactions with the tab grid view controller and the BVC at
either end of the transition. That will also be addressed in follow-
up CLs.

Bug:  804539 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: If38c185b3c510b3665f5761ebce67ea4ad36d6dc
Reviewed-on: https://chromium-review.googlesource.com/975610
Commit-Queue: Mark Cogan <marq@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545502}
[modify] https://crrev.com/43c79ea79708e960b6bd859c2b6765e63052fcbc/ios/chrome/app/main_controller.mm
[modify] https://crrev.com/43c79ea79708e960b6bd859c2b6765e63052fcbc/ios/chrome/browser/ui/tab_grid/tab_grid_transition_handler.mm
[modify] https://crrev.com/43c79ea79708e960b6bd859c2b6765e63052fcbc/ios/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm
[modify] https://crrev.com/43c79ea79708e960b6bd859c2b6765e63052fcbc/ios/chrome/browser/ui/tab_grid/transitions/grid_to_visible_tab_animator.h
[modify] https://crrev.com/43c79ea79708e960b6bd859c2b6765e63052fcbc/ios/chrome/browser/ui/tab_grid/transitions/grid_to_visible_tab_animator.mm
[modify] https://crrev.com/43c79ea79708e960b6bd859c2b6765e63052fcbc/ios/chrome/browser/ui/tab_grid/transitions/grid_transition_animation.h
[modify] https://crrev.com/43c79ea79708e960b6bd859c2b6765e63052fcbc/ios/chrome/browser/ui/tab_grid/transitions/grid_transition_animation.mm
[modify] https://crrev.com/43c79ea79708e960b6bd859c2b6765e63052fcbc/ios/chrome/browser/ui/tab_grid/transitions/tab_to_grid_animator.mm

Mark is this task now completed?

The NextAction date has arrived: 2018-03-28

This is built; any clean-up work will be part of the polish tasks.

The NextAction date has arrived: 2018-04-25