[iOS][MF] Keyboard dismissal

This CL presents the popover in the same window as the accessory button.
By doing this it won't be hidden by the keyboard and it will dissapear
when the user interacts with the keyboard.

Bug: 845472
Cq-Include-Trybots: luci.chromium.try:ios-simulator-cronet;luci.chromium.try:ios-simulator-full-configs
Change-Id: I5ab3243cb8d6281105d77387b384692086e260b9
Reviewed-on: https://chromium-review.googlesource.com/c/1268342
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600191}
3 files changed