Handle AssistantMiniView pressed event.

Pressing Assistant UI when it is in mini state should cause it to
re-expand. We only do this when NOT using stylus input modality.

The implementation uses a delegate pattern analogously to what was
done previously with CaptionBar(Delegate).

Bug: b:110986383
Change-Id: I3dfdb85542b9ae591e3ec3f2f74eb4e7065a3859
Reviewed-on: https://chromium-review.googlesource.com/1137483
Commit-Queue: David Black <dmblack@google.com>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575528}
5 files changed