Merge from origin/emacs-25

Merge from origin/emacs-25

ea26c8a * lisp/net/browse-url.el (browse-url-default-browser): Lower
        priority of non-free Chrome.
0fac75f Improve the custom type of some user options.
2df0e04 Highlight CSS variables with variable name face
3cf5e81 * lisp/gnus/gnus-kill.el (gnus-winconf-kill-file): Not
        user-serviceable.
2a5233c Mark some user options that can get evalled as risky.
39b166f Disable DebPrint in sys_read on MS-Windows
9fd0189 ;Fix ChangeLog entry
4bb7233 Fix typos in Introduction to Emacs Lisp manual