The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a7531d73addc36e1fc7c9830493b65d6031ff3df

commit a7531d73addc36e1fc7c9830493b65d6031ff3df
Author: Kurt Horimoto <kkhorimoto@chromium.org>
Date: Fri Sep 15 22:40:56 2017

[iOS Clean] Wait for consumer to stop before starting next overlay.

This helps eliminate the issue where one overlay is attempted to be
started while another is still being dismissed.

This CL also adds a test util function to wait for overlay dismissal
since this change adds an asynchronous element to the overlay
scheduling.

Bug:  765822 
Change-Id: I658b630f7f46fcc925df12807d2ccc34ff5b83ab
Reviewed-on: https://chromium-review.googlesource.com/618513
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#502413}
[modify] https://crrev.com/a7531d73addc36e1fc7c9830493b65d6031ff3df/ios/chrome/browser/ui/coordinators/browser_coordinator.mm
[modify] https://crrev.com/a7531d73addc36e1fc7c9830493b65d6031ff3df/ios/chrome/browser/ui/coordinators/browser_coordinator_test_util.h
[modify] https://crrev.com/a7531d73addc36e1fc7c9830493b65d6031ff3df/ios/chrome/browser/ui/coordinators/browser_coordinator_test_util.mm
[modify] https://crrev.com/a7531d73addc36e1fc7c9830493b65d6031ff3df/ios/clean/chrome/browser/ui/overlays/overlay_coordinator.mm
[modify] https://crrev.com/a7531d73addc36e1fc7c9830493b65d6031ff3df/ios/clean/chrome/browser/ui/overlays/overlay_scheduler_unittest.mm
[modify] https://crrev.com/a7531d73addc36e1fc7c9830493b65d6031ff3df/ios/clean/chrome/browser/ui/overlays/test_helpers/test_overlay_queue.h
[modify] https://crrev.com/a7531d73addc36e1fc7c9830493b65d6031ff3df/ios/clean/chrome/browser/ui/overlays/test_helpers/test_overlay_queue.mm