Linux: include zlib headers to avoid a breakage with libpng-1.5
Linux: include zlib headers to avoid a breakage with libpng-1.5

See http://bugs.gentoo.org/show_bug.cgi?id=365841

BUG=none
Review URL: http://codereview.chromium.org/6969030

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@85146 0039d316-1c4b-4281-b951-d872f2087c98

ropik/chromium,ropik/chromium,gavinp/chromium,gavinp/chromium,adobe/chromium,gavinp/chromium,adobe/chromium,gavinp/chromium,gavinp/chromium,yitian134/chromium,gavinp/chromium,adobe/chromium,ropik/chromium,adobe/chromium,yitian134/chromium,yitian134/chromium,adobe/chromium,ropik/chromium,ropik/chromium,gavinp/chromium,yitian134/chromium,yitian134/chromium,yitian134/chromium,adobe/chromium,yitian134/chromium,ropik/chromium,adobe/chromium,adobe/chromium,yitian134/chromium,ropik/chromium,yitian134/chromium,adobe/chromium,gavinp/chromium,ropik/chromium,gavinp/chromium,adobe/chromium,yitian134/chromium,ropik/chromium,gavinp/chromium,adobe/chromium