[iOS] Add missing comment to SettingsTableViewController

This CL adds some missing context to the DUMP_WILL_BE_CHECK
that was previously added in the SettingsTableViewController
implementation of the account manager service observer's
shutdown event.

Bug: 328252472, 40926211
Change-Id: Ib175260b06f56c06726bc7866b158871c7a81c80
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5353556
Reviewed-by: Jérôme Lebel <jlebel@chromium.org>
Commit-Queue: Guillaume Jenkins <gujen@google.com>
Auto-Submit: Guillaume Jenkins <gujen@google.com>
Cr-Commit-Position: refs/heads/main@{#1270298}
diff --git a/ios/chrome/browser/ui/settings/settings_table_view_controller.mm b/ios/chrome/browser/ui/settings/settings_table_view_controller.mm
index 0afb326..adf39b7 100644
--- a/ios/chrome/browser/ui/settings/settings_table_view_controller.mm
+++ b/ios/chrome/browser/ui/settings/settings_table_view_controller.mm
@@ -2250,6 +2250,9 @@
 
 - (void)onChromeAccountManagerServiceShutdown:
     (ChromeAccountManagerService*)accountManagerService {
+  // TODO(crbug.com/40926211): settingsWillBeDismissed must be called before the
+  // AccountManagerService is destroyed. Switch to DCHECK if the number of
+  // reports is low.
   DUMP_WILL_BE_CHECK(!_accountManagerServiceObserver.get());
 }