InstallAppProviderService now processes install and delete events one at a
time, where InstalledAppCacheUpdater made a batch of changes which it ran
all at once. This means that InstallAppProviderService will send out a
flood of notifications when first initializing, since it will index every
single installed app and send a notification for each one. This makes the
GUI lock up. This commit puts a rate limit on those notifications if they
start coming fast. They are limited to one per second.
906a26414a