In scss-mode, Font Lock hangs on particular instances of Sass lists.
To see an example of this, paste the following into a buffer, and
activate scss-mode + font-lock-mode:

$list: (
    ('string', #000000, #fff)
    ('string', #000000, #fff)
    ('string', #000000, #fff)
    ('string', #000000, #fff)
    ('string', #000000, #fff)
    ('string', #000000, #fff)
);

Font Lock hangs, and I find that I have to press C-g a number of times
to be able to continue editing.


In GNU Emacs 25.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.6)
 of 2015-08-10 on x240
Repository revision: a9bb9d8fc22417d1fafd8001d89a91c33c8b39ec
Windowing system distributor `The X.Org Foundation', version 
11.0.11702000
System Description:	Debian GNU/Linux testing (stretch)

Configured features:
XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS NOTIFY LIBXML2 FREETYPE XFT
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: SCSS