lod@ PTAL

viewWillTransitionToSize (in the widget's view controller) gets called after the view changes sizes. This seems like a bug (I'm seeing similar behavior in one of Google Maps' widgets for example). The only alternative I can think of is to have a fixed top margin for the compact portion of the widget at all times. This has pros and cons (pros: animation works, cons: appearance with non-default text size as set in accessibility won't be as good)

If this is a bug in iOS 11, could you file a radar and let Pink know please ?

Issue 755745 has been merged into this issue.

Radar filed for this issue: https://bugreport.apple.com/web/?problemID=34161108

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5a5293bee4e4e9b7ecc1685fa8877931ac37fed8

commit 5a5293bee4e4e9b7ecc1685fa8877931ac37fed8
Author: Elodie Banel <lod@google.com>
Date: Fri Sep 01 09:50:06 2017

Fix animation bug in widget.

The layoutIfNeeded call is generally required as per Apple. It was
working in iOS10 without it but not in iOS11.

Bug:  756849 
Change-Id: Iee1d066928abb809f84714fa138dcfa09a4a5059
Reviewed-on: https://chromium-review.googlesource.com/645956
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Elodie Banel <lod@chromium.org>
Cr-Commit-Position: refs/heads/master@{#499161}
[modify] https://crrev.com/5a5293bee4e4e9b7ecc1685fa8877931ac37fed8/ios/chrome/content_widget_extension/content_widget_view_controller.mm
[modify] https://crrev.com/5a5293bee4e4e9b7ecc1685fa8877931ac37fed8/ios/chrome/search_widget_extension/search_widget_view_controller.mm

Radar closed and solution provided by Apple engineers (basically: I was missing a call to layoutifneeded and the fact that it worked in ios10 was just dumb luck).