Move referrer stripping into GURL::GetAsReferrer().

This patch moves the code that removes username, password and ref parts
of the url from http referrers into GURL::GetAsReferrer().

BUG=340295

Review URL: https://codereview.chromium.org/185133005

git-svn-id: https://src.chromium.org/chrome/trunk/src/url@258392 4ff67af0-8c30-449e-8e8b-ad334ec8d88c