Introduce CrosapiTestBase.

CrosapiTestBase is for Ash-side crosapi testing.
By separating the test process from the Ash-chrome process, we can test
the behavior of crosapi only on Ash-side.

When introducing tests using this, you need to bind the crosapi you use (e.g., FileManager and NetworkChange).

Bug: 1357441
Change-Id: Id4ab8fda4b1cc01cd497303b9593995a1f1f8ce1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3886122
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Eriko Kurimoto <elkurin@chromium.org>
Commit-Queue: Anna Sato <annasato@google.com>
Reviewed-by: Oksana Zhuravlova <oksamyt@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1048886}