Remove stale TODO + unnecessary if-guard in Pipeline::DoSeek().
Remove stale TODO + unnecessary if-guard in Pipeline::DoSeek().

If we call DoSeek() without a demuxer we've clearly got issues as we shouldn't be seeking without a demuxer so crashing is preferable.

BUG=none
TEST=none
TBR=acolwell

Review URL: https://chromiumcodereview.appspot.com/10694125

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@146024 0039d316-1c4b-4281-b951-d872f2087c98

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