Cancel proxy request when context is about to change in SocketStream.
Cancel proxy request when context is about to change in SocketStream.

If SocketStream is deleted while ResolvProxy is running, proxy service
might access SocketStream's member fields, such as proxy_info_, after
SocketStream is deleted, so it would cause crash like
http://crash/reportdetail?reportid=40166b9529ce6b74

In SocketStream destructor, it will set context to NULL, so it will
cancel proxy request if pac_request_ is not NULL.

BUG=46750
TEST=none

Review URL: http://codereview.chromium.org/2852034

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@51351 0039d316-1c4b-4281-b951-d872f2087c98

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