fix gm on Mac, and Linux buildbot build, by adding zlib source to third_party 
http://codereview.appspot.com/4620047/

I will try to find a better way to keep all this working (remove zlib and
libpng from third_party)



git-svn-id: http://skia.googlecode.com/svn/trunk@1595 2bbb7eff-a529-9590-31e7-b0007b416f81
233 files changed