[Mfill Android]Hide the sheet when the automatic generation button is pressed

For the case in which only the accessory bar is show, pressing the generation
button results in the keyboard being hidden. Since the accessory sheet aims
to behave like the keyboard, it should also be hidden on button tap.

This also mitigates the unresponsive button issue, described in the bug.

Bug: 962959
Change-Id: Ib7b2900e31420352a6e733608e238caeaa04e4f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1612914
Commit-Queue: Ioana Pandele <ioanap@chromium.org>
Reviewed-by: Friedrich [CET] <fhorschig@chromium.org>
Reviewed-by: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660362}
4 files changed