exo: Initialize activatable and ignored_by_shelf properly.
exo: Initialize activatable and ignored_by_shelf properly.

Initialize this state properly in case it takes some time before
a first commit arrives.

BUG=549781
TEST=exo_unittests

Review URL: https://codereview.chromium.org/1879113002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#386780}

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