Copied  issue chromium:822328  from  issue chromium:820410 

Why does this bug description say polish animation details. This should only be about the RTL fix. 

Notes:
The issue is in 2 places:
1) TabGridPageControl slider position only goes in LTR direction.
2) The currentPage calculation is only done in LTR order. 

Both issues are due to direct frame position access, which is not 
RTL friendly. 

The way to fix this is to check for RTL and flip the position. 
There are two ways to check for RTL. 
1) The Chrome approach is //base/i18n/rtl.h
2) The other is iOS idiomatic: https://developer.apple.com/documentation/uikit/uiview/1622480-userinterfacelayoutdirectionfors

> 1) TabGridPageControl slider position only goes in LTR direction.

This is incorrect. Setting the slider position to 0 positions it at the leading side; setting it to 1 positions it at the trailing side. 

> The way to fix this is to check for RTL and flip the position. 

Generally speaking this is the last resort for RTL support in iOS Chrome. In this case (setting the contentOffset of the scroll view), layout constraints can't be used, but the utility functions in rtl_geometry.h (or an extension of them) should be.

Hi All,

Thanks for reporting.
Removing UI>Localization from this bug. This is a localization issue.

Regards! 

Pri-0 bugs are critical regressions or serious emergencies, and this bug has not been updated in three days. Could you please provide an update, or adjust the priority to a more appropriate level if applicable?

If a fix is in active development, please set the status to Started.

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The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cc989fc90f630fd86d7be24c4d9afdd415a736f3

commit cc989fc90f630fd86d7be24c4d9afdd415a736f3
Author: Mark Cogan <marq@google.com>
Date: Tue Apr 17 14:19:56 2018

[iOS] RTL paging fixes for Tab Grid.

Fix various paging isssues in RTL with the Tab Grid.

- Tapping the page control, or otherwise setting |currentPage| on the
  TabGridViewController will set the correct offset for the scroll view.

- Scrolling the view will set the correct page.

- Scrolling the view moves the page control correctly.

Bug:  822328 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Ic8f53c894fd4388b97d82093ac35ad675caa87a5
Reviewed-on: https://chromium-review.googlesource.com/1013927
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551317}
[modify] https://crrev.com/cc989fc90f630fd86d7be24c4d9afdd415a736f3/ios/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm

Tested in 68.0.3405.0 Canary, iPhone 7 iOS11.4 beta 2
In this scenario bug is still showing:
1. Launch app
2. Change device mode to landscape
3. Tap on tab switcher

Observe: In RTL, the paging on the tab grid is incorrect.
https://drive.google.com/file/d/1gz9MGiltso-DXV1ZxwxqnVryYBVy3-4C/view

The NextAction date has arrived: 2018-06-06

This actually isn't RTL-specific any more. If the device has rotated since the last time the tab grid was displayed (including on launch), the scroll position may be incorrect.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b7f319368b344d61bb6c09f28f76c7fa45cfbe5a

commit b7f319368b344d61bb6c09f28f76c7fa45cfbe5a
Author: Mark Cogan <marq@google.com>
Date: Mon Jun 11 15:31:25 2018

[iOS] Correct scroll positioning when tab grid layout rotates.

This CL corrects situations where the tab grid may position its scroll
offset incorrectly when handling a size class transition.

The issue was that none of the call points for updating the scroll
position (via setting self.currentPage) were guaranteed to take place
after the scroll view's width had changed.

This CL moves some of those call points into -viewWillLayoutSubviews,
so that whenever the scroll view width changes it will be repositioned
correctly. Since this change should often not be animated, the
currentPage setter now doesn't animate by default, and a
-setCurrentPage:animated: method is available when animations are
needed.

Bug:  822328 
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I36833314fc6d79d32cfddf9be8dacbeabc8ba4b9
Reviewed-on: https://chromium-review.googlesource.com/1093990
Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566008}
[modify] https://crrev.com/b7f319368b344d61bb6c09f28f76c7fa45cfbe5a/ios/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm

Verified in 69.0.3464.0 Canary on iPhone8plus(iOS 11.4 beta), iPhone 7(iOS 10.3.3) and iPad Air(iOS 11.4 beta)

After device rotation tab grid paging looks good

Link to video:
https://drive.google.com/file/d/1vyPgDupamWua-TQfTGyf8dErbW7J9AQp/view?usp=sharing