arc: Provide API to control Play Store state from autotests

This provides required API to read and set Play Store state from
autotests since old settings page will deprecate soon and new MD
settings don't provide reliable way to access Play Store settings.

BUG=694081
TEST=Manually, together with
     https://chromium-review.googlesource.com/c/470707/

Review-Url: https://codereview.chromium.org/2801173002
Cr-Commit-Position: refs/heads/master@{#464735}
8 files changed