Remove observer when removing delegate, in Instant.
Remove observer when removing delegate, in Instant.

I believe the crash (see bug link) is caused because we remove the delegate
connection, but we never stop observing the WebContents. I haven't reproduced
the crash, but I think this should fix the root cause. I've put in a bandaid as
well, which might be redundant, but good for safety. Will remove it once I can
confirm the fix works.

BUG=141875
R=sky@chromium.org
TEST=This type of crash (see bug) should go away.

Review URL: https://chromiumcodereview.appspot.com/10829284

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@151173 0039d316-1c4b-4281-b951-d872f2087c98

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