This patch modifies DownloadSpamProtection and DownloadIntegration so
that each window will track blocked spam downloads separately. (Which
shouldn't affect permissions.) When a download is blocked, the helper
app service dispatches a notification, passing the relevant browsing
context and URL to DownloadIntegration. Then it passes the window and
URL to the singleton DownloadSpamProtection. That maps all the windows
to objects that carry the spam download objects. This allows us to only
show blocked spam downloads in the downloads panel of the window from
which they were triggered.
Differential Revision: https://phabricator.services.mozilla.com/D148092
34b247cb72