Removes a bogus DCHECK. This DCHECK is bogus for two reasons:
Removes a bogus DCHECK. This DCHECK is bogus for two reasons:

. it's checking a field that hasn't been set yet, hence the sporadic
  failure.
. It shouldn't check delegate either as inside this class it's
  possible to supply NULL.

I've removed it entirely and added a comment.

BUG=5914
TEST=right click on the tab strip and make sure you don't get a
     DCHECK. Because this relies on random data, it's too hard to
     write a test for this, additionally I'm sure once we run the
     interactive ui tests under Purify this'll be covered.

Review URL: http://codereview.chromium.org/17439

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@7777 0039d316-1c4b-4281-b951-d872f2087c98

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