Create helper method to wait for bookmarks to load.

Multiple tests were manually waiting for bookmarks to load.

Bug: 638674
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Id6ac5f242478119aaaee673f8ac8d671a3638ad3
Reviewed-on: https://chromium-review.googlesource.com/777393
Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Mike Baxley <baxley@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#517587}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 9c63560adf74e026015c7b0e3ff86256adeb77f3
6 files changed