Fix is https://chromium-review.googlesource.com/c/chromium/src/+/741599

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c28e695161d2e3db018dd78c1d0b743439e1a4d8

commit c28e695161d2e3db018dd78c1d0b743439e1a4d8
Author: Jean-François Geyelin <jif@chromium.org>
Date: Fri Oct 27 18:53:14 2017

Have the StackView's scrollview be positioned with autolayout.

Bug:  779032 ,  765408 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I6731b515f1ae2e7f33dde48f9f4ab84334af530b
Reviewed-on: https://chromium-review.googlesource.com/741599
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512256}
[modify] https://crrev.com/c28e695161d2e3db018dd78c1d0b743439e1a4d8/ios/chrome/browser/ui/stack_view/stack_view_controller.mm

This bug requires manual review: M63 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), gkihumba@(ChromeOS), govind@(Desktop)

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I don't think we want to cherry-pick this to M63 branch because we have decided to not enable the SACT flag for M63 release. Looking at the code, the real change is bracketed inside the test for SACT flag.

Verified in M64.0.3282.75 beta
iOS: 11.2.5
Device: iPhoneX

Stack View is displayed correctly after rotating the device.