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: de016e52bd170d2d4f2344f9bf92d50478b649e0@22646 0039d316-1c4b-4281-b951-d872f2087c98

yitian134/chromium,adobe/chromium,ropik/chromium,yitian134/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,gavinp/chromium,adobe/chromium,adobe/chromium,Crystalnix/house-of-life-chromium,adobe/chromium,gavinp/chromium,yitian134/chromium,ropik/chromium,gavinp/chromium,ropik/chromium,adobe/chromium,gavinp/chromium,ropik/chromium,yitian134/chromium,adobe/chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,ropik/chromium,adobe/chromium,gavinp/chromium,adobe/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,ropik/chromium,ropik/chromium,adobe/chromium,gavinp/chromium,gavinp/chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,adobe/chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,Crystalnix/house-of-life-chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,gavinp/chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,adobe/chromium,Crystalnix/house-of-life-chromium