Another bug caused by GObject floating references :')
The GVariant returned by builder_end() is floating, and the way
g_variant_builder_add_value works is that it _only_ takes a reference if
floating.
So basically if you have a RefPtr<GVariant> with a floating reference,
then pass it to g_variant_builder_add_value, the reference is "stolen",
but RefPtr doesn't know about it.
It really sucks.
Differential Revision: https://phabricator.services.mozilla.com/D190240
d22609c3bc