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This CL handles the situation when default app is not available
after Arc starts. In this case, default app entry is removed from
the app launcher.

BUG=b/31934494
TEST=Extended unit tests
TEST=Manually on device.
     Normal flow: Start Arc by clicking default app icon. Spinning
     item appears in shelf for the starting app. Play Store starts,
     spiining item stil exists and installtion stars (view in
     notification). Once default app is installed, it automatically
     pops up and spinning item is replaced with normal icon.
     App is not available flow: Repeat steps above. Installation
     for default app does not appear and spinning item is removed
     from shelf soon after. Default app is also removed from the
     app launcher.
     Re-sign in. In both cases default app state is preserved.

Review-Url: https://codereview.chromium.org/2601323002
Cr-Commit-Position: refs/heads/master@{#442073}