Nit comments about other parts of the OpenJDK 9 HTTP Client API.

Should URLs perhaps be represented as Strings to get around restrictions by
the URL/URI classes? Has the disadvantages that it weakens the type, but is
the approach used by cornet [1].

[1] https://chromium.googlesource.com/chromium/src/+/lkgr/components/cronet/

This issue has been filed to capture comments raised by tobiast at google dot com, see
http://mail.openjdk.java.net/pipermail/net-dev/2017-July/010872.html