Fix segmentation fault in trace_subscriber_stdio.cc.
Fix segmentation fault in trace_subscriber_stdio.cc.

This is part of Chrome for Android upstreaming.

This crash happens when the output trace file can't be opened. It is due to the
trace buffer's output callback not being set in case the file can't be opened.
Even if TraceResultBuffer::Start() is not called, the output callback still
needs to be set since it is used by TraceResultBuffer::AddFragment().

BUG=152867

Review URL: https://chromiumcodereview.appspot.com/11038062

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@160669 0039d316-1c4b-4281-b951-d872f2087c98

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