sync: speculative fix for bug 165561
sync: speculative fix for bug 165561

The SyncManager will stop the scheduler as part of StopSyncingForShutdown, which
happens well before things like the invalidator are torn down / told to stop
interacting with the scheduler.  As such, we can wind up scheduling nudges on a lame
duck scheduler.  Some of the stacks associated with 165561 clearly show browser
shutdown happening on the UI thread and OnIncomingInvalidation happening on the
sync thread, which will crash on a second invocation as pending_nudge will be
set to a job that is dropped by ScheduleSyncSessionJob.

BUG=165561


Review URL: https://chromiumcodereview.appspot.com/11827013

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@175945 0039d316-1c4b-4281-b951-d872f2087c98

markYoungH/chromium.src,Jonekee/chromium.src,TheTypoMaster/chromium-crosswalk,jaruba/chromium.src,TheTypoMaster/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,bright-sparks/chromium-spacewalk,M4sse/chromium.src,TheTypoMaster/chromium-crosswalk,Pluto-tv/chromium-crosswalk,anirudhSK/chromium,Fireblend/chromium-crosswalk,nacl-webkit/chrome_deps,hujiajie/pa-chromium,axinging/chromium-crosswalk,ltilve/chromium,dednal/chromium.src,mogoweb/chromium-crosswalk,dednal/chromium.src,pozdnyakov/chromium-crosswalk,ChromiumWebApps/chromium,fujunwei/chromium-crosswalk,axinging/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,mogoweb/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,jaruba/chromium.src,Jonekee/chromium.src,Chilledheart/chromium,M4sse/chromium.src,patrickm/chromium.src,crosswalk-project/chromium-crosswalk-efl,dushu1203/chromium.src,Chilledheart/chromium,ltilve/chromium,dednal/chromium.src,bright-sparks/chromium-spacewalk,mohamed--abdel-maksoud/chromium.src,ChromiumWebApps/chromium,Pluto-tv/chromium-crosswalk,bright-sparks/chromium-spacewalk,hgl888/chromium-crosswalk,dednal/chromium.src,hujiajie/pa-chromium,hgl888/chromium-crosswalk-efl,hgl888/chromium-crosswalk-efl,jaruba/chromium.src,dushu1203/chromium.src,anirudhSK/chromium,Fireblend/chromium-crosswalk,markYoungH/chromium.src,zcbenz/cefode-chromium,littlstar/chromium.src,littlstar/chromium.src,mogoweb/chromium-crosswalk,mogoweb/chromium-crosswalk,pozdnyakov/chromium-crosswalk,Pluto-tv/chromium-crosswalk,anirudhSK/chromium,Chilledheart/chromium,PeterWangIntel/chromium-crosswalk,anirudhSK/chromium,anirudhSK/chromium,dushu1203/chromium.src,Jonekee/chromium.src,anirudhSK/chromium,M4sse/chromium.src,pozdnyakov/chromium-crosswalk,krieger-od/nwjs_chromium.src,Pluto-tv/chromium-crosswalk,jaruba/chromium.src,dednal/chromium.src,axinging/chromium-crosswalk,Fireblend/chromium-crosswalk,ChromiumWebApps/chromium,Pluto-tv/chromium-crosswalk,nacl-webkit/chrome_deps,markYoungH/chromium.src,zcbenz/cefode-chromium,PeterWangIntel/chromium-crosswalk,dushu1203/chromium.src,ondra-novak/chromium.src,markYoungH/chromium.src,axinging/chromium-crosswalk,ChromiumWebApps/chromium,ChromiumWebApps/chromium,jaruba/chromium.src,M4sse/chromium.src,anirudhSK/chromium,krieger-od/nwjs_chromium.src,mohamed--abdel-maksoud/chromium.src,nacl-webkit/chrome_deps,dushu1203/chromium.src,hgl888/chromium-crosswalk-efl,fujunwei/chromium-crosswalk,timopulkkinen/BubbleFish,mogoweb/chromium-crosswalk,patrickm/chromium.src,markYoungH/chromium.src,mogoweb/chromium-crosswalk,markYoungH/chromium.src,ondra-novak/chromium.src,nacl-webkit/chrome_deps,PeterWangIntel/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,chuan9/chromium-crosswalk,fujunwei/chromium-crosswalk,zcbenz/cefode-chromium,pozdnyakov/chromium-crosswalk,jaruba/chromium.src,dushu1203/chromium.src,littlstar/chromium.src,mohamed--abdel-maksoud/chromium.src,ltilve/chromium,PeterWangIntel/chromium-crosswalk,anirudhSK/chromium,ltilve/chromium,hgl888/chromium-crosswalk,hgl888/chromium-crosswalk,fujunwei/chromium-crosswalk,anirudhSK/chromium,Chilledheart/chromium,crosswalk-project/chromium-crosswalk-efl,dushu1203/chromium.src,Just-D/chromium-1,ChromiumWebApps/chromium,krieger-od/nwjs_chromium.src,pozdnyakov/chromium-crosswalk,ondra-novak/chromium.src,Jonekee/chromium.src,markYoungH/chromium.src,ondra-novak/chromium.src,dednal/chromium.src,mogoweb/chromium-crosswalk,M4sse/chromium.src,jaruba/chromium.src,axinging/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,jaruba/chromium.src,TheTypoMaster/chromium-crosswalk,krieger-od/nwjs_chromium.src,M4sse/chromium.src,crosswalk-project/chromium-crosswalk-efl,markYoungH/chromium.src,crosswalk-project/chromium-crosswalk-efl,ChromiumWebApps/chromium,fujunwei/chromium-crosswalk,hujiajie/pa-chromium,krieger-od/nwjs_chromium.src,zcbenz/cefode-chromium,Chilledheart/chromium,axinging/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,Just-D/chromium-1,timopulkkinen/BubbleFish,littlstar/chromium.src,chuan9/chromium-crosswalk,fujunwei/chromium-crosswalk,littlstar/chromium.src,dushu1203/chromium.src,dushu1203/chromium.src,mogoweb/chromium-crosswalk,fujunwei/chromium-crosswalk,pozdnyakov/chromium-crosswalk,dednal/chromium.src,chuan9/chromium-crosswalk,nacl-webkit/chrome_deps,nacl-webkit/chrome_deps,mohamed--abdel-maksoud/chromium.src,markYoungH/chromium.src,fujunwei/chromium-crosswalk,hgl888/chromium-crosswalk,timopulkkinen/BubbleFish,ltilve/chromium,crosswalk-project/chromium-crosswalk-efl,krieger-od/nwjs_chromium.src,chuan9/chromium-crosswalk,Fireblend/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,timopulkkinen/BubbleFish,dushu1203/chromium.src,ondra-novak/chromium.src,bright-sparks/chromium-spacewalk,pozdnyakov/chromium-crosswalk,hujiajie/pa-chromium,nacl-webkit/chrome_deps,Pluto-tv/chromium-crosswalk,markYoungH/chromium.src,hujiajie/pa-chromium,anirudhSK/chromium,jaruba/chromium.src,ltilve/chromium,jaruba/chromium.src,Jonekee/chromium.src,mohamed--abdel-maksoud/chromium.src,hgl88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