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This CL adds plumbing for the TestController crosapi. This is only
available on Linux (non-device). It's used to provide a synchronization
primitive between crosapi and Wayland, and basic automation
capabilities. This is to support more full-fledged crosapi tests.

This CL moves the previous implementation of
WaitForLacrosToBeAvailableInAsh back into
screen_manager_lacros_browsertest.cc. This CL adds the new methods
WaitForWindowToBeAvailableInAsh and SendAndWaitForMouseClick.

Change-Id: Ia497c13f2b38af62eba3618cdca526b0206b32ec
Bug: 1157946
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587707
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836984}