arc: Make Play Store item persistance in shelf.
This also shares item with OptIn UI.
BUG=b/28485354
TEST=Manually on device. Play Store icon exists always on shelf.
when Arc is not OptedIn, clicking this icon opens OptIn UI
and this shelf icon behaives as ordinal Platform app. Clicking
on it minimizes/shows UI. Play Store is automatically started
on OptIn flow finishes. Once Play Store started, there is no
additional icon for Android app. It reuses the same shelf
item. Menu in all cases does not have pin/unpin option. If
Chromebook is opted in already, this just starts/activates
PlayStore window and no additional item in shelf is created.
Review-Url: https://codereview.chromium.org/1973603002
Cr-Commit-Position: refs/heads/master@{#394444}
20 files changed
