GNOME Shell browser plugin

[Michael Catanzaro <mcatanzaro gnome org>]

Hi,

I am planning to propose blacklisting the GNOME browser plugin in
WebKit, because it has been causing crashes and hangs for several
years, and we don't know how to fix it. My recent commit apparently
didn't help; when we do WebKit updates in Fedora, users regularly
complain in the comments that extensions.gnome.org still causes crashes
or hangs, and we hear this on IRC often as well. I'm planning to
propose making this change effective in WebKitGTK+ 2.12 (March 2016),
so there is time to migrate to something else, but not time to keep
ignoring the issue. Ideally we would not need to do this, and either
fix or delete the plugin in gnome-shell instead.

This only matters for users running under X11; users running under
Wayland already have no support for NPAPI plugins. Since we're planning
to switch to Wayland by default in Fedora 24, this change would have no
impact on Fedora users: extensions.gnome.org will be broken there (in
Epiphany) no matter what.

Of course, it's bad to break extensions.gnome.org by blacklisting the
plugin, but I'd rather the site be totally broken but Epiphany stable
than the site work sometimes but crash or hang the web process often.
extensions.gnome.org is already broken in Chrome because Chrome got rid
of all NPAPI plugins a while back, and it will soon be broken in
Firefox because Firefox has decided to ban all except Flash by the end
of 2016, so you could see this as incentive to either migrate to
something else (it wouldn't be hard to add the plugin code to Epiphany
itself, but that won't work for Firefox/Chrome) or shut the thing down
before Firefox shuts it down for us.

We're going to continue to support other NPAPI plugins in WebKit
indefinitely when running in X11; the GNOME shell plugin is special
only because it's installed by default and causing problems for many
users.

Michael