Linux: use 'settings' for system libpng.
Linux: use 'settings' for system libpng.

It turns out that 'settings' is the correct GYP target type for this
sort of thing. Thanks to Evan for pointing out my mistake.


git-svn-id: http://src.chromium.org/svn/trunk/src@22646 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: c566192954dfa8073ba0893087a0fb457da6c9a7
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser