[ios] Fix tab grid layout issue in multi-windows

Bug: 1096035,1076852
Change-Id: I386b8127fd0aed588226b6068553e086a7bba18c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2273158Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: David Jean <djean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#783854}

ios/chrome/browser/ui/tab_grid/tab_grid_bottom_toolbar.mm

@@ -204,10 +204,10 @@
   // |-traitCollectionDidChange:| is not properly called when the view rotates
   // while it is in a ViewController deeper in the ViewController hierarchy. Use
   // self.traitCollection since iOS 13 where the bug is fixed in UIKit.
-  return UIApplication.sharedApplication.keyWindow.traitCollection
-                 .verticalSizeClass == UIUserInterfaceSizeClassRegular &&
-         UIApplication.sharedApplication.keyWindow.traitCollection
-                 .horizontalSizeClass == UIUserInterfaceSizeClassCompact;
+  return self.window.traitCollection.verticalSizeClass ==
+             UIUserInterfaceSizeClassRegular &&
+         self.window.traitCollection.horizontalSizeClass ==
+             UIUserInterfaceSizeClassCompact;
 }
 
 @end