Fix issue with disposed tasks in .Net 4.0.
Fix issue with disposed tasks in .Net 4.0.

AJDev77/CefSharp,Livit/CefSharp,ITGlobal/CefSharp,illfang/CefSharp,jamespearce2006/CefSharp,NumbersInternational/CefSharp,VioletLife/CefSharp,illfang/CefSharp,jamespearce2006/CefSharp,rlmcneary2/CefSharp,illfang/CefSharp,Livit/CefSharp,wangzheng888520/CefSharp,haozhouxu/CefSharp,Haraguroicha/CefSharp,twxstar/CefSharp,NumbersInternational/CefSharp,jamespearce2006/CefSharp,joshvera/CefSharp,Haraguroicha/CefSharp,Haraguroicha/CefSharp,dga711/CefSharp,jamespearce2006/CefSharp,NumbersInternational/CefSharp,joshvera/CefSharp,NumbersInternational/CefSharp,dga711/CefSharp,ITGlobal/CefSharp,Haraguroicha/CefSharp,gregmartinhtc/CefSharp,VioletLife/CefSharp,VioletLife/CefSharp,ITGlobal/CefSharp,haozhouxu/CefSharp,wangzheng888520/CefSharp,Haraguroicha/CefSharp,gregmartinhtc/CefSharp,AJDev77/CefSharp,haozhouxu/CefSharp,Livit/CefSharp,gregmartinhtc/CefSharp,twxstar/CefSharp,rlmcneary2/CefSharp,dga711/CefSharp,illfang/CefSharp,VioletLife/CefSharp,rlmcneary2/CefSharp,ITGlobal/CefSharp,AJDev77/CefSharp,wangzheng888520/CefSharp,rlmcneary2/CefSharp,jamespearce2006/CefSharp,joshvera/CefSharp,dga711/CefSharp,twxstar/CefSharp,gregmartinhtc/CefSharp,wangzheng888520/CefSharp,Livit/CefSharp,joshvera/CefSharp,haozhouxu/CefSharp,AJDev77/CefSharp,twxstar/CefSharp