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The associated code moved to PersistentNotificationHandler, so let's
make sure that the tests follow. More functionality will be built on top
so this'll form a nice base.

Change-Id: Ib40bfdfbc3efb4d63506e8e8791370a70fa8e3f9
Reviewed-on: https://chromium-review.googlesource.com/1181904Reviewed-by: Tim Volodine <timvolodine@chromium.org>
Commit-Queue: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584714}