There is already a method for reproducibly generating an int based on
a the contents of a String, thanks to @pserwylo for finding it! So
urlString.hashCode() is used as the ID for Notifications and the
DownloaderService queue (msg.what). This entirely replaces the
QUEUE_WHATS hack. Both requestCode and msg.what just need to be
unique int, and that value can always be generated by the urlString.
This also fixes a bug preventing removing correct URL from Downloader queue.
b66810944fec802aa119c0e5ec8b7875930a2c22 made a change that breaks removing
the correct item from the queue. The `what` value must be fetched based on
urlString and fed to serviceHandler.removeMessages(what). The commit made
it use the `what` value from the last item that was queued. Those will
often be different things.
This also removes all stopForeground(true) calls except for the one in
onDestroy(). The nature of an IntentService, which DownloaderService
is basically a copy of, is to quit running once it is no longer
processing Intents. That is also the time to remove the notification.
44b703a7d2