gistfile1.el

;; modified http://www.emacswiki.org/emacs/TinyUrl
(require 'thingatpt)
(defun my-get-shorter-bug-url(longer-uri)
  (cond ((string-match "bugs.webkit.org" longer-uri)
	 (let ((num-start (string-match "[[:digit:]]" longer-uri)))
	   (concat "http://webkit.org/b/" (substring longer-uri num-start))))
	((string-match "http://code.google.com/p/chromium/issues" longer-uri)
	 (let ((num-start (string-match "[[:digit:]]" longer-uri)))
	   (concat "http://crbug.com/" (substring longer-uri num-start))))
	((error (concat longer-uri " is not bug url")))))

(defun my-shorten-bug-url()
  (interactive)
  (let ((bounds (bounds-of-thing-at-point 'url)))
    (when bounds
      (let* ((long-url (buffer-substring
                        (car bounds) (cdr bounds)))
             (short-url (my-get-shorter-bug-url long-url)))
	(save-excursion
          (goto-char (car bounds))
          (replace-string long-url short-url nil (car bounds) (cdr bounds)))))))

(global-set-key (kbd "C-c S") 'my-shorten-bug-url)