Functions that decoded ie7 structures to extract per-URL username and password assumed there will only be one such pair for a URL. Changed to work with URLs for which there are several sets of credentials stored.

BUG=305241
TEST=IE7PasswordTest.*

Review URL: https://codereview.chromium.org/26465006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228180 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228180