GitLab

Add GetDlcState method to client as well as fake client and associated unittests.

TEST=b:172223380
BUG=autoninja -C out/Default/ unit_tests &&  ./out/Default/unit_tests --gtest_filter=*Dlc*


dlcservice: 
Change-Id: I6f26c75e7d73447d14e724558a1f381198de88d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2540367Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Vyshu Khota <vyshu@google.com>
Cr-Commit-Position: refs/heads/master@{#827881}