passwords, native_backend_gnome_x: Get rid of variadic arguments

Currently, queries to Gnome's keyring for credential data are done with
functions using variadic arguments to pass all search criteria.

Once we introduce fuzzy matching for this platform, we will need to selectively
leave out the "signon_realm" search criterion. With variadic calls, this
means duplicating the whole call, with one argument left out.

This CL switches to the equivalent GNOME API calls which use argument lists
instead of variadic parameters. With that, individual arguments can be left
out without touching the rest of the code.

BUG=324291

Review URL: https://codereview.chromium.org/101593008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241540 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241540