[Sync] Don't DCHECK if we can't find the window for a tab

chrome/browser/ui/sync/browser_synced_window_delegate.cc

Index: chrome/browser/ui/sync/browser_synced_window_delegate.cc
diff --git a/chrome/browser/ui/sync/browser_synced_window_delegate.cc b/chrome/browser/ui/sync/browser_synced_window_delegate.cc
index 7809aa006af612b6aa1743b45649eb35e046b486..2057582f86a38b78f556472da95cfe2adea9365b 100644
--- a/chrome/browser/ui/sync/browser_synced_window_delegate.cc
+++ b/chrome/browser/ui/sync/browser_synced_window_delegate.cc
@@ -47,7 +47,8 @@ bool BrowserSyncedWindowDelegate::IsTabPinned(
     if (tab == current)
       return browser_->tab_strip_model()->IsTabPinned(i);
   }
-  NOTREACHED();
+  // The window and tab are not always updated atomically, so it's possible
+  // one of the values was stale. We'll retry later, just ignore for now.
   return false;
 }