bug#19270: 25.0.50; make PDF mode in EWW customizable

[Ivan Shmakov <ivan@siamics.net>]

>>>>> Sebastian Wiesner <swiesner@lunaryorn.com> writes:

 > Currently EWW uses `doc-view-mode' to view PDF data.  This choice is
 > hard-coded in `eww-display-pdf' and cannot be customized.

 > Some users (e. g. http://emacs.stackexchange.com/q/4089/227) however
 > desire to use alternative PDF modes, e. g. PDF Tools from
 > https://github.com/axot/pdf-tools.

 > Please make the PDF mode used by EWW customizable, so that users
 > don't have to resort to advices in order to change it.

	My suggestion would be to replace the (cond …) form in
	eww-render with something as flexible as:

   (let ((try-render (run-hook-with-args-until-success
                      eww-render-hook buffer url headers)))
     (if try-render
         (with-current-buffer try-render
           (when (derived-mode-p 'eww-mode)
             (plist-put eww-data :url url)
             (eww-update-header-line-format)
             (setq eww-history-position 0)
             (run-hooks 'eww-after-render-hook)))
       (error "No handler for Content-Type: %s (%s)"
              (car content-type) url)))

	Where eww-render-hook is a customizable hook with the default
	value chosen so to imitate the current behavior.

	(Also, I’d like to suggest replacing the hard-coded input
	handling in the ‘eww’ command proper with a similar
	eww-input-hook, so to be able to add support for urn:ietf:,
	‘!whatever’, etc.)

-- 
FSF associate member #7257  np. Man on the Silver Mountain — Dio  … 230E 334A