Normalize placeholder URL
When the session is saved, "ephy-about:overview" URL is substituted with
"about:overview". When the session is later restored and delay loading
is used, ephy_web_view_set_placeholder()
is called to show an empty
page until the requested page is fully loaded.
But since ephy_web_view_set_placeholder()
does not normalize the
passed URL and "about:overview" is not listed in do_not_show_address
,
it appears in the URL bar as is.
Fixes #1918 (closed)