The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b12391c6b25d1b47c83d1333e2d7f8fe2c55ed20

commit b12391c6b25d1b47c83d1333e2d7f8fe2c55ed20
Author: Mark Cogan <marq@google.com>
Date: Fri Dec 29 12:04:44 2017

[iOS] Fix language selection popup edge cases.

This CL fixes several edge cases for the language selection popup; these all involve
circumstances where the popup should be implicitly dismissed.

In order to facilitate this, the LanguageSelectionHandler has a -dismissLanguageSelector
method added.

In ChromeIOSTranslateClent::WebStateDestroyed, a call to -dismissLanguageSelector is added. This
handles the case where the tab showing the selector is closed.

In BVC's tabModel:didChangeActiveTab:previousTab:atIndex: method, a call to
-dismissLanguageSelector is made if there's an infobar container. This handles the case where the
active tab changes while the selector is displayed, dismissing it.

LanguageSelectionCoordinator implements -dismissLanguageSelector by dismissing the contained
view controller without animation.

VerticalAnimationContainer has some added DCHECKS and logic to handle and/or warn about some
cases that can come up when dismissing the container when its base view controller is outside
of the view hierarchy.

Bug:  797787 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Id2714d92441f4cea0b6aaeeb48d0751d8e3df465
Reviewed-on: https://chromium-review.googlesource.com/845679
Reviewed-by: Mark Cogan <marq@chromium.org>
Reviewed-by: Stepan Khapugin <stkhapugin@chromium.org>
Commit-Queue: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526369}
[modify] https://crrev.com/b12391c6b25d1b47c83d1333e2d7f8fe2c55ed20/ios/chrome/browser/translate/chrome_ios_translate_client.mm
[modify] https://crrev.com/b12391c6b25d1b47c83d1333e2d7f8fe2c55ed20/ios/chrome/browser/translate/language_selection_handler.h
[modify] https://crrev.com/b12391c6b25d1b47c83d1333e2d7f8fe2c55ed20/ios/chrome/browser/ui/browser_view_controller.mm
[modify] https://crrev.com/b12391c6b25d1b47c83d1333e2d7f8fe2c55ed20/ios/chrome/browser/ui/presenters/contained_presenter.h
[modify] https://crrev.com/b12391c6b25d1b47c83d1333e2d7f8fe2c55ed20/ios/chrome/browser/ui/presenters/vertical_animation_container.mm
[modify] https://crrev.com/b12391c6b25d1b47c83d1333e2d7f8fe2c55ed20/ios/chrome/browser/ui/translate/language_selection_coordinator.mm

Issue 798050 has been merged into this issue.

Verified based on the steps reported.
Device: iPhone6s, iPhoneX
iOS: 10.3.3, 11.2.5 beta#3
Version: M65.0.3311.0 canary.

Note: Issue 798050 is marked as RBS for M64. So please check if this fix needs tobe merged into M64.

Mark does this need to be merged still? 

Marking as RBS for M64 as Issue 798050 is.

This was marked as RBS when it was already in a verified state and therefore did not really block M64. This fix was never merged into M64 as far as I can tell since there are some reports on M64 stable. Mark, how critical is this?

It's not a crasher, but there are some pretty ugly UI states that can result. This is a lot of code to merge into 64 at this stage though.

[Auto-generated comment by a script] We noticed that this issue is targeted for M-64; it appears the fix may have landed after branch point, meaning a merge might be required. Please confirm if a merge is required here - if so add Merge-Request-64 label, otherwise remove Merge-TBD label. Thanks.

Mark, do we have the fix in M65 though?

Yup!