Use a reasonable default pthread stack size on Mac OS X.
Use a reasonable default pthread stack size on Mac OS X.

Mac OS X uses a fixed default stack size of 512kB, which is too small for some
purposes. glibc on Linux uses ulimit -s, which is both a more reasonable thing
to do, and is generally set to a rational limit, such as 8MB.

BUG=43422
TEST=None really on the trunk. On the Mac 375 branch, using the .pac file on
     the bug, Chrome should not crash on startup.
Review URL: http://codereview.chromium.org/2035007

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@46717 0039d316-1c4b-4281-b951-d872f2087c98

zcbenz/cefode-chromium,TheTypoMaster/chromium-crosswalk,keishi/chromium,timopulkkinen/BubbleFish,hgl888/chromium-crosswalk-efl,Fireblend/chromium-crosswalk,fujunwei/chromium-crosswalk,ChromiumWebApps/chromium,jaruba/chromium.src,keishi/chromium,crosswalk-project/chromium-crosswalk-efl,robclark/chromium,ondra-novak/chromium.src,ChromiumWebApps/chromium,pozdnyakov/chromium-crosswalk,Chilledheart/chromium,mohamed--abdel-maksoud/chromium.src,chuan9/chromium-crosswalk,Just-D/chromium-1,keishi/chromium,anirudhSK/chromium,Pluto-tv/chromium-crosswalk,nacl-webkit/chrome_deps,pozdnyakov/chromium-crosswalk,ltilve/chromium,markYoungH/chromium.src,fujunwei/chromium-crosswalk,anirudhSK/chromium,patrickm/chromium.src,hgl888/chromium-crosswalk-efl,anirudhSK/chromium,hgl888/chromium-crosswalk-efl,PeterWangIntel/chromium-crosswalk,chuan9/chromium-crosswalk,Fireblend/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,rogerwang/chromium,robclark/chromium,pozdnyakov/chromium-crosswalk,hujiajie/pa-chromium,Just-D/chromium-1,dednal/chromium.src,rogerwang/chromium,anirudhSK/chromium,axinging/chromium-crosswalk,zcbenz/cefode-chromium,patrickm/chromium.src,bright-sparks/chromium-spacewalk,pozdnyakov/chromium-crosswalk,ChromiumWebApps/chromium,ChromiumWebApps/chromium,ChromiumWebApps/chromium,jaruba/chromium.src,dushu1203/chromium.src,Jonekee/chromium.src,markYoungH/chromium.src,chuan9/chromium-crosswalk,patrickm/chromium.src,anirudhSK/chromium,hgl888/chromium-crosswalk,ondra-novak/chromium.src,crosswalk-project/chromium-crosswalk-efl,krieger-od/nwjs_chromium.src,zcbenz/cefode-chromium,nacl-webkit/chrome_deps,littlstar/chromium.src,patrickm/chromium.src,hgl888/chromium-crosswalk,rogerwang/chromium,pozdnyakov/chromium-crosswalk,timopulkkinen/BubbleFish,littlstar/chromium.src,Chilledheart/chromium,hgl888/chromium-crosswalk,hujiajie/pa-chromium,ltilve/chromium,pozdnyakov/chromium-crosswalk,ondra-novak/chromium.src,Chilledheart/chromium,markYoungH/chromium.src,zcbenz/cefode-chromium,hujiajie/pa-chromium,krieger-od/nwjs_chromium.src,axinging/chromium-crosswalk,zcbenz/cefode-chromium,mohamed--abdel-maksoud/chromium.src,jaruba/chromium.src,anirudhSK/chromium,Just-D/chromium-1,littlstar/chromium.src,markYoungH/chromium.src,axinging/chromium-crosswalk,ltilve/chromium,jaruba/chromium.src,anirudhSK/chromium,Pluto-tv/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,Pluto-tv/chromium-crosswalk,Fireblend/chromium-crosswalk,mogoweb/chromium-crosswalk,jaruba/chromium.src,bright-sparks/chromium-spacewalk,junmin-zhu/chromium-rivertrail,crosswalk-project/chromium-crosswalk-efl,krieger-od/nwjs_chromium.src,pozdnyakov/chromium-crosswalk,markYoungH/chromium.src,dednal/chromium.src,dednal/chromium.src,hgl888/chromium-crosswalk-efl,mohamed--abdel-maksoud/chromium.src,dushu1203/chromium.src,robclark/chromium,Pluto-tv/chromium-crosswalk,ondra-novak/chromium.src,rogerwang/chromium,mogoweb/chromium-crosswalk,keishi/chromium,junmin-zhu/chromium-rivertrail,timopulkkinen/BubbleFish,Jonekee/chromium.src,Just-D/chromium-1,junmin-zhu/chromium-rivertrail,PeterWangIntel/chromium-crosswalk,Pluto-tv/chromium-crosswalk,ChromiumWebApps/chromium,dednal/chromium.src,TheTypoMaster/chromium-crosswalk,junmin-zhu/chromium-rivertrail,junmin-zhu/chromium-rivertrail,hgl888/chromium-crosswalk,bright-sparks/chromium-spacewalk,krieger-od/nwjs_chromium.src,dushu1203/chromium.src,keishi/chromium,robclark/chromium,ondra-novak/chromium.src,zcbenz/cefode-chromium,Pluto-tv/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,Fireblend/chromium-crosswalk,M4sse/chromium.src,anirudhSK/chromium,hgl888/chromium-crosswalk,M4sse/chromium.src,littlstar/chromium.src,krieger-od/nwjs_chromium.src,jaruba/chromium.src,Just-D/chromium-1,axinging/chromium-crosswalk,robclark/chromium,TheTypoMaster/chromium-crosswalk,junmin-zhu/chromium-rivertrail,Chilledheart/chromium,Fireblend/chromium-crosswalk,hgl888/chromium-crosswalk,chuan9/chromium-crosswalk,Fireblend/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,timopulkkinen/BubbleFish,TheTypoMaster/chromium-crosswalk,dednal/chromium.src,hujiajie/pa-chromium,fujunwei/chromium-crosswalk,bright-sparks/chromium-spacewalk,bright-sparks/chromium-spacewalk,ChromiumWebApps/chromium,pozdnyakov/chromium-crosswalk,jaruba/chromium.src,Jonekee/chromium.src,keishi/chromium,anirudhSK/chromium,dednal/chromium.src,M4sse/chromium.src,crosswalk-project/chromium-crosswalk-efl,ChromiumWebApps/chromium,mohamed--abdel-maksoud/chromium.src,littlstar/chromium.src,pozdnyakov/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,Just-D/chromium-1,rogerwang/chromium,crosswalk-project/chromium-crosswalk-efl,rogerwang/chromium,PeterWangIntel/chromium-crosswalk,dednal/chromium.src,krieger-od/nwjs_chromium.src,mogoweb/chromium-crosswalk,ondra-novak/chromium.src,Just-D/chromium-1,robclark/chromium,ltilve/chromium,nacl-webkit/chrome_deps,Chilledheart/chromium,mohamed--abdel-maksoud/chromium.src,timopulkkinen/Bu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