Revert 184551
Revert 184551

There was a massive regression on Mac memory usage between 184543 and 184560.
This looks like the only likely culprit.  Sorry for the trouble.
See http://build.chromium.org/f/chromium/perf/mac-release-memory/memory/report.html?history=50&rev=184560

> Turn on threaded compositing in OSX for continuous builds. 
> 
> BUG=172015
> TBR=vangelis
> 
> 
> Review URL: https://chromiumcodereview.appspot.com/12251016

TBR=ccameron@chromium.org
Review URL: https://codereview.chromium.org/12335099

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@184671 0039d316-1c4b-4281-b951-d872f2087c98

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