This looks like a tasking tracking bug as well.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c82006414aa7d03f2b8034b4e0de2db3094a7233

commit c82006414aa7d03f2b8034b4e0de2db3094a7233
Author: Eugene But <eugenebut@google.com>
Date: Fri Dec 07 19:25:53 2018

IOSChromeLocalSessionEventRouter does not subclass from GlobalWebStateObserver.

IOSChromeLocalSessionEventRouter will observe multiple WebState objects
without using deprecated GlobalWebStateObserver.

Also removed browser state check in OnWebStateChange. This check was needed
because each WSO callback was called for both BrowserState objects. So the
router had to check if the call belongs to correct browser state. After this
CL there are no extra calls, hence no need for check.

Bug: 910894, 782269,  720786 
Change-Id: Ie25ae62efea9edd4a981800d1a43b6ef28b35b14
Reviewed-on: https://chromium-review.googlesource.com/c/1359863
Commit-Queue: Eugene But <eugenebut@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614779}
[modify] https://crrev.com/c82006414aa7d03f2b8034b4e0de2db3094a7233/ios/chrome/browser/sync/BUILD.gn
[rename] https://crrev.com/c82006414aa7d03f2b8034b4e0de2db3094a7233/ios/chrome/browser/sync/session_sync_service_factory.mm
[modify] https://crrev.com/c82006414aa7d03f2b8034b4e0de2db3094a7233/ios/chrome/browser/sync/sessions/BUILD.gn
[modify] https://crrev.com/c82006414aa7d03f2b8034b4e0de2db3094a7233/ios/chrome/browser/sync/sessions/ios_chrome_local_session_event_router.h
[modify] https://crrev.com/c82006414aa7d03f2b8034b4e0de2db3094a7233/ios/chrome/browser/sync/sessions/ios_chrome_local_session_event_router.mm

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/74bc9ffe09805e919717a59a745885099198626e

commit 74bc9ffe09805e919717a59a745885099198626e
Author: Eugene But <eugenebut@google.com>
Date: Wed Jan 09 09:09:43 2019

Remove unused code from GlobalWebStateObserver.

Bug: 782269
Change-Id: I02e842c5d19710a3a7368d0da139dd1844100ddf
Reviewed-on: https://chromium-review.googlesource.com/c/1400957
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621083}
[modify] https://crrev.com/74bc9ffe09805e919717a59a745885099198626e/ios/web/public/web_state/global_web_state_observer.h
[modify] https://crrev.com/74bc9ffe09805e919717a59a745885099198626e/ios/web/web_state/global_web_state_event_tracker.h
[modify] https://crrev.com/74bc9ffe09805e919717a59a745885099198626e/ios/web/web_state/global_web_state_event_tracker.mm
[modify] https://crrev.com/74bc9ffe09805e919717a59a745885099198626e/ios/web/web_state/web_state_impl_unittest.mm