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This CL creates gn targets for lacros tast tests, and the main
motivation is to run lacros tast tests on Chromium CI.

Bug: 1158590
Change-Id: I783779c3386a39743b8227367189b0b87832b9dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2606188
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Cr-Commit-Position: refs/heads/master@{#844127}