Minor cleanups to variation_service.cc.
Minor cleanups to variation_service.cc.

- DCHECK(false) -> NOTREACHED()
- Extract date conversion to a helper function

BUG=none
TEST=none

Review URL: https://chromiumcodereview.appspot.com/10375055

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@137739 0039d316-1c4b-4281-b951-d872f2087c98

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