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When calling |RegisterNonPersistentNotificationListener| with an existed
notification id, it will first dispatch a close event to old notification
and set new listener into listener map.

Currently the new listener is replaced immediately after calling
|DispatchNonPersistentCloseEvent|, since it's an asynchronize call,
it will remove the replaced listener unexpectedly, instead of removing
the original listener.

To fix this, we can postpone listener replacement after the close event
finish it's cleaning job. For new created notification, the listener can
be set immediately due to there is no close event need to be dispatched.

Bug: 880266, 898486
Change-Id: I370d77386cf1a6636f368f1785d92d362a3b4263
Reviewed-on: https://chromium-review.googlesource.com/c/1303898Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604203}