Account for localhost. (with trailing dot) in origin resolving

See whatwg/url#693 for context.

Author: annevk

fetch.bs

@@ -2362,7 +2362,8 @@ functionality.
  « <var>origin</var>'s <a for=origin>host</a> ».
 
  <li><p>If <var>origin</var>'s <a for=origin>host</a>'s <a for=host>public suffix</a> is
- "<code>localhost</code>", then return « <code>::1</code>, <code>127.0.0.1</code> ».
+ "<code>localhost</code>" or "<code>localhost.</code>", then return « <code>::1</code>,
+ <code>127.0.0.1</code> ».
 
  <li>
   <p>Perform an <a>implementation-defined</a> operation to turn <var>origin</var> into a