Use our native JS error system in the "extension system" API, only
using the signal/log-based error reporting at the last mile. Additionally,
delete the directory if loading the extension failed, and report the error
back over DBus.
https://bugzilla.gnome.org/show_bug.cgi?id=679099
Instead of using the 'extension-state-changed' signal to relay errors,
use DBus's native error mechanism to inform the method caller that the
call has failed. This requires making the method actually asynchronous
so that we don't block the browser, which is stuck waiting for a reply
from the browser plugin. To ensure this, we need to modify the browser
plugin API to ensure its extesion installation method is asynchronous.
Additionally, this lets us remove the awful, broken hacks that we used
when a user clicked the "Cancel" button, replacing it by a DBus return
value.
https://bugzilla.gnome.org/show_bug.cgi?id=679099
When the extension downloader was originally designed, the information
downloading part was inserted at the last minute, along with the modal
dialog as a security feature to make sure an extension didn't silently
get installed on the user's machines either due to a security issue in
the browser-plugin, or an XSS issue on the extensions website. Correct
the mistake I made when writing the code; instead of dropping an error
on the floor, log it correctly. This "bug" has already bitten a number
of users who forgot to configure proxy settings in the control center.
https://bugzilla.gnome.org/show_bug.cgi?id=679099
