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This CL enables presentation in iPads as a popover instead of above the keyboard.
This follows the UX design for Manual Fallback.
- Makes sure the accessory bar for iPad is always added when Manual Fallback is Enabled.
- The responsibility of not showing the accessory bar when other UI is presenting the
keyboard is now fully own by the input accessory bar view controller.

Bug: 845472
Cq-Include-Trybots: luci.chromium.try:ios-simulator-cronet;luci.chromium.try:ios-simulator-full-configs
Change-Id: Ife13cc44b4912084ccb10376ee9c53039dc00548
Reviewed-on: https://chromium-review.googlesource.com/c/1256793
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600131}