[Linux] do not register widget extension the app is not widget
[Linux] do not register widget extension the app is not widget

If the application is not a widget, access to exposed "widget"
object will cause crash.

BUG=https://crosswalk-project.org/jira/browse/XWALK-3575

marcuspridham/crosswalk,pk-sam/crosswalk,hgl888/crosswalk-efl,hgl888/crosswalk-efl,lincsoon/crosswalk,baleboy/crosswalk,jondong/crosswalk,marcuspridham/crosswalk,tomatell/crosswalk,tedshroyer/crosswalk,ZhengXinCN/crosswalk,bestwpw/crosswalk,axinging/crosswalk,jondong/crosswalk,DonnaWuDongxia/crosswalk,pk-sam/crosswalk,stonegithubs/crosswalk,chuan9/crosswalk,jpike88/crosswalk,rakuco/crosswalk,axinging/crosswalk,amaniak/crosswalk,RafuCater/crosswalk,RafuCater/crosswalk,Bysmyyr/crosswalk,RafuCater/crosswalk,zliang7/crosswalk,Pluto-tv/crosswalk,Bysmyyr/crosswalk,zeropool/crosswalk,siovene/crosswalk,jondwillis/crosswalk,heke123/crosswalk,tedshroyer/crosswalk,lincsoon/crosswalk,lincsoon/crosswalk,zliang7/crosswalk,xzhan96/crosswalk,crosswalk-project/crosswalk-efl,amaniak/crosswalk,hgl888/crosswalk-efl,xzhan96/crosswalk,xzhan96/crosswalk,Pluto-tv/crosswalk,ZhengXinCN/crosswalk,siovene/crosswalk,hgl888/crosswalk-efl,crosswalk-project/crosswalk-efl,xzhan96/crosswalk,chuan9/crosswalk,weiyirong/crosswalk-1,lincsoon/crosswalk,pk-sam/crosswalk,Bysmyyr/crosswalk,bestwpw/crosswalk,zeropool/crosswalk,minggangw/crosswalk,axinging/crosswalk,jondwillis/crosswalk,darktears/crosswalk,ZhengXinCN/crosswalk,dreamsxin/crosswalk,ZhengXinCN/crosswalk,weiyirong/crosswalk-1,darktears/crosswalk,hgl888/crosswalk-efl,crosswalk-project/crosswalk,zeropool/crosswalk,XiaosongWei/crosswalk,RafuCater/crosswalk,xzhan96/crosswalk,baleboy/crosswalk,lincsoon/crosswalk,axinging/crosswalk,baleboy/crosswalk,chuan9/crosswalk,jondong/crosswalk,marcuspridham/crosswalk,Bysmyyr/crosswalk,zeropool/crosswalk,minggangw/crosswalk,lincsoon/crosswalk,amaniak/crosswalk,marcuspridham/crosswalk,siovene/crosswalk,amaniak/crosswalk,crosswalk-project/crosswalk-efl,rakuco/crosswalk,darktears/crosswalk,heke123/crosswalk,baleboy/crosswalk,RafuCater/crosswalk,lincsoon/crosswalk,chuan9/crosswalk,tedshroyer/crosswalk,marcuspridham/crosswalk,bestwpw/crosswalk,ZhengXinCN/crosswalk,axinging/crosswalk,amaniak/crosswalk,crosswalk-project/crosswalk-efl,crosswalk-project/crosswalk,heke123/crosswalk,hgl888/crosswalk,siovene/crosswalk,PeterWangIntel/crosswalk,stonegithubs/crosswalk,Pluto-tv/crosswalk,Pluto-tv/crosswalk,Pluto-tv/crosswalk,baleboy/crosswalk,Bysmyyr/crosswalk,darktears/crosswalk,siovene/crosswalk,amaniak/crosswalk,baleboy/crosswalk,tomatell/crosswalk,DonnaWuDongxia/crosswalk,DonnaWuDongxia/crosswalk,siovene/crosswalk,Bysmyyr/crosswalk,dreamsxin/crosswalk,minggangw/crosswalk,heke123/crosswalk,zliang7/crosswalk,crosswalk-project/crosswalk-efl,jpike88/crosswalk,PeterWangIntel/crosswalk,jondwillis/crosswalk,alex-zhang/crosswalk,darktears/crosswalk,tomatell/crosswalk,dreamsxin/crosswalk,tomatell/crosswalk,DonnaWuDongxia/crosswalk,siovene/crosswalk,ZhengXinCN/crosswalk,baleboy/crosswalk,jpike88/crosswalk,weiyirong/crosswalk-1,zliang7/crosswalk,PeterWangIntel/crosswalk,jondwillis/crosswalk,hgl888/crosswalk,tedshroyer/crosswalk,baleboy/crosswalk,jondwillis/crosswalk,stonegithubs/crosswalk,XiaosongWei/crosswalk,crosswalk-project/crosswalk,jondwillis/crosswalk,alex-zhang/crosswalk,bestwpw/crosswalk,xzhan96/crosswalk,alex-zhang/crosswalk,axinging/crosswalk,tedshroyer/crosswalk,chuan9/crosswalk,PeterWangIntel/crosswalk,tedshroyer/crosswalk,xzhan96/crosswalk,xzhan96/crosswalk,DonnaWuDongxia/crosswalk,marcuspridham/crosswalk,DonnaWuDongxia/crosswalk,heke123/crosswalk,crosswalk-project/crosswalk,hgl888/crosswalk,jpike88/crosswalk,crosswalk-project/crosswalk-efl,stonegithubs/crosswalk,stonegithubs/crosswalk,zliang7/crosswalk,chuan9/crosswalk,XiaosongWei/crosswalk,weiyirong/crosswalk-1,darktears/crosswalk,rakuco/crosswalk,XiaosongWei/crosswalk,zliang7/crosswalk,marcuspridham/crosswalk,rakuco/crosswalk,crosswalk-project/crosswalk,bestwpw/crosswalk,weiyirong/crosswalk-1,jpike88/crosswalk,XiaosongWei/crosswalk,minggangw/crosswalk,jondong/crosswalk,rakuco/crosswalk,tedshroyer/crosswalk,rakuco/crosswalk,tomatell/crosswalk,stonegithubs/crosswalk,pk-sam/crosswalk,ZhengXinCN/crosswalk,amaniak/crosswalk,heke123/crosswalk,tomatell/crosswalk,weiyirong/crosswalk-1,darktears/crosswalk,axinging/crosswalk,minggangw/crosswalk,darktears/crosswalk,DonnaWuDongxia/crosswalk,dreamsxin/crosswalk,weiyirong/crosswalk-1,hgl888/crosswalk,alex-zhang/crosswalk,crosswalk-project/crosswalk,hgl888/crosswalk,stonegithubs/crosswalk,crosswalk-project/crosswalk,jondong/crosswalk,PeterWangIntel/crosswalk,zliang7/crosswalk,crosswalk-project/crosswalk,XiaosongWei/crosswalk,PeterWangIntel/crosswalk,zeropool/crosswalk,RafuCater/crosswalk,hgl888/crosswalk-efl,jondong/crosswalk,minggangw/crosswalk,bestwpw/crosswalk,rakuco/crosswalk,lincsoon/crosswalk,jondong/crosswalk,crosswalk-project/crosswalk-efl,Bysmyyr/crosswalk,Pluto-tv/crosswalk,pk-sam/crosswalk,rakuco/crosswalk,chuan9/crosswalk,minggangw/crosswalk,hgl888/crosswalk,tomatell/crosswalk,bestwpw/crosswalk,jpike88/crosswalk,alex-zhang/crosswalk,dreamsxin/crosswalk,alex-zhang/crosswalk,zeropool/crosswalk,marcuspridham/crosswalk,hgl888/crosswalk,pk-sam/crosswalk,jondwillis/crosswalk,alex-zhang/crosswalk,pk-sam/crosswalk,PeterWangIntel/crosswalk,heke123/crosswalk,dreamsxin/crosswalk,Pluto-tv/crosswalk,heke123/crosswalk,jondong/crosswalk,dreamsxin/crosswalk,jpike88/crosswalk,hgl888/crosswalk-efl,RafuCater/crosswalk,Bysmyyr/crosswalk,zliang7/crosswalk,zeropool/crosswalk,XiaosongWei/crosswalk,hgl888/crosswalk,minggangw/crosswalk