Use Echo for delivering the notification to the last
user who edited the filter.
Much boilerplate.
Change-Id: I7a46a03b4f15de20902ec70c62fb4fe750096842
Depends-On: If585b14a6dd6fb8c7d2c3bee1f20d9d08eaac706
Also fix a bug in FilterProfiler. It would attempt to reset
stats for global filters but we do not record them (yet?).
Change-Id: I0228d8c85dab146deb877dfce506f1e8e7711a9f
This will ease adding new watchers, for instance to send Echo
notifications (see T179495 and T100892).
For now, this is just boilerplate, and converting EmergencyWatcher to
the new interface.
Change-Id: I18d62aba53471202b709cdb19033b1729c5c25b4