GitLab

This class inherits from |AssistantInteractionSubscriber| and provides
a dummy implementation of all the methods, so that test classes can
derive from this and only implement what they need.

It also adds a |mojom::Remote| that every test class needs.

Bug: b/151800188
Change-Id: I1f06f180e2f99c76a09171122777e24561e0a562
Tests: Ran existing unittests
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2128838Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Commit-Queue: Jeroen Dhollander <jeroendh@google.com>
Cr-Commit-Position: refs/heads/master@{#756354}