Similar to the async updates to alertList, async the sort updates since they also modify from within an observer. Additionally, preserve expansion properties and propagate them up to the new header of the group as shifting the list around you end up with funny highlights and partially broken functionality.
Similar to the async updates to alertList, async the sort
updates since they also modify from within an observer.
Additionally, preserve expansion properties and propagate
them up to the new header of the group as shifting the list
around you end up with funny highlights and partially
broken functionality.

BUG=catapult:#2545

Review-Url: https://codereview.chromium.org/2182203002

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