[iOS][MF] Add a11y labels for the accessory icons

Bug: 845472
Change-Id: I47898430b16721084ec836c2d4627ccf1db7c0c3
Reviewed-on: https://chromium-review.googlesource.com/c/1338181
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609288}
7 files changed