[Runtime] Fix getting the wrong value from widget API toString method.
[Runtime] Fix getting the wrong value from widget API toString method.

According to W3C widget API specification, the widget.toString() method
should return "[object Widget]" value.

BUG=XWALK-1667

jondong/crosswalk,DonnaWuDongxia/crosswalk,mrunalk/crosswalk,myroot/crosswalk,stonegithubs/crosswalk,qjia7/crosswalk,myroot/crosswalk,stonegithubs/crosswalk,lincsoon/crosswalk,tomatell/crosswalk,crosswalk-project/crosswalk,dreamsxin/crosswalk,jpike88/crosswalk,hgl888/crosswalk-efl,tedshroyer/crosswalk,Pluto-tv/crosswalk,alex-zhang/crosswalk,jondwillis/crosswalk,jondong/crosswalk,marcuspridham/crosswalk,zliang7/crosswalk,mrunalk/crosswalk,huningxin/crosswalk,tomatell/crosswalk,fujunwei/crosswalk,stonegithubs/crosswalk,DonnaWuDongxia/crosswalk,XiaosongWei/crosswalk,PeterWangIntel/crosswalk,leonhsl/crosswalk,jondong/crosswalk,RafuCater/crosswalk,siovene/crosswalk,qjia7/crosswalk,alex-zhang/crosswalk,XiaosongWei/crosswalk,Pluto-tv/crosswalk,hgl888/crosswalk,minggangw/crosswalk,xzhan96/crosswalk,marcuspridham/crosswalk,siovene/crosswalk,heke123/crosswalk,jondong/crosswalk,leonhsl/crosswalk,dreamsxin/crosswalk,crosswalk-project/crosswalk-efl,ZhengXinCN/crosswalk,zliang7/crosswalk,alex-zhang/crosswalk,stonegithubs/crosswalk,XiaosongWei/crosswalk,siovene/crosswalk,bestwpw/crosswalk,crosswalk-project/crosswalk,huningxin/crosswalk,RafuCater/crosswalk,fujunwei/crosswalk,dreamsxin/crosswalk,Bysmyyr/crosswalk,siovene/crosswalk,baleboy/crosswalk,chuan9/crosswalk,pk-sam/crosswalk,lincsoon/crosswalk,zeropool/crosswalk,zliang7/crosswalk,siovene/crosswalk,crosswalk-project/crosswalk,tedshroyer/crosswalk,hgl888/crosswalk,jondong/crosswalk,leonhsl/crosswalk,weiyirong/crosswalk-1,RafuCater/crosswalk,chinakids/crosswalk,pk-sam/crosswalk,rakuco/crosswalk,lincsoon/crosswalk,axinging/crosswalk,jondwillis/crosswalk,Bysmyyr/crosswalk,lincsoon/crosswalk,pk-sam/crosswalk,tomatell/crosswalk,jondwillis/crosswalk,zliang7/crosswalk,DonnaWuDongxia/crosswalk,TheDirtyCalvinist/spacewalk,minggangw/crosswalk,alex-zhang/crosswalk,Pluto-tv/crosswalk,chuan9/crosswalk,crosswalk-project/crosswalk,pk-sam/crosswalk,jpike88/crosswalk,hgl888/crosswalk-efl,weiyirong/crosswalk-1,xzhan96/crosswalk,mrunalk/crosswalk,stonegithubs/crosswalk,minggangw/crosswalk,myroot/crosswalk,zeropool/crosswalk,XiaosongWei/crosswalk,fujunwei/crosswalk,baleboy/crosswalk,RafuCater/crosswalk,zeropool/crosswalk,hgl888/crosswalk,bestwpw/crosswalk,zeropool/crosswalk,fujunwei/crosswalk,baleboy/crosswalk,tedshroyer/crosswalk,tomatell/crosswalk,heke123/crosswalk,rakuco/crosswalk,fujunwei/crosswalk,darktears/crosswalk,rakuco/crosswalk,Bysmyyr/crosswalk,crosswalk-project/crosswalk,chuan9/crosswalk,zliang7/crosswalk,heke123/crosswalk,darktears/crosswalk,xzhan96/crosswalk,zeropool/crosswalk,rakuco/crosswalk,mrunalk/crosswalk,huningxin/crosswalk,heke123/crosswalk,dreamsxin/crosswalk,baleboy/crosswalk,rakuco/crosswalk,mrunalk/crosswalk,Bysmyyr/crosswalk,XiaosongWei/crosswalk,RafuCater/crosswalk,chinakids/crosswalk,tomatell/crosswalk,baleboy/crosswalk,axinging/crosswalk,TheDirtyCalvinist/spacewalk,RafuCater/crosswalk,heke123/crosswalk,bestwpw/crosswalk,PeterWangIntel/crosswalk,darktears/crosswalk,amaniak/crosswalk,baleboy/crosswalk,jondong/crosswalk,marcuspridham/crosswalk,Bysmyyr/crosswalk,marcuspridham/crosswalk,RafuCater/crosswalk,xzhan96/crosswalk,Pluto-tv/crosswalk,chinakids/crosswalk,TheDirtyCalvinist/spacewalk,TheDirtyCalvinist/spacewalk,darktears/crosswalk,pk-sam/crosswalk,darktears/crosswalk,weiyirong/crosswalk-1,weiyirong/crosswalk-1,tedshroyer/crosswalk,minggangw/crosswalk,rakuco/crosswalk,tedshroyer/crosswalk,minggangw/crosswalk,jondong/crosswalk,crosswalk-project/crosswalk-efl,jondwillis/crosswalk,hgl888/crosswalk,ZhengXinCN/crosswalk,hgl888/crosswalk-efl,jondong/crosswalk,amaniak/crosswalk,DonnaWuDongxia/crosswalk,chuan9/crosswalk,alex-zhang/crosswalk,dreamsxin/crosswalk,alex-zhang/crosswalk,axinging/crosswalk,marcuspridham/crosswalk,chinakids/crosswalk,lincsoon/crosswalk,minggangw/crosswalk,XiaosongWei/crosswalk,xzhan96/crosswalk,XiaosongWei/crosswalk,weiyirong/crosswalk-1,jpike88/crosswalk,pk-sam/crosswalk,minggangw/crosswalk,DonnaWuDongxia/crosswalk,Bysmyyr/crosswalk,chinakids/crosswalk,bestwpw/crosswalk,amaniak/crosswalk,qjia7/crosswalk,bestwpw/crosswalk,tomatell/crosswalk,crosswalk-project/crosswalk,Bysmyyr/crosswalk,xzhan96/crosswalk,PeterWangIntel/crosswalk,amaniak/crosswalk,huningxin/crosswalk,leonhsl/crosswalk,chuan9/crosswalk,DonnaWuDongxia/crosswalk,marcuspridham/crosswalk,chinakids/crosswalk,hgl888/crosswalk,jondwillis/crosswalk,Pluto-tv/crosswalk,baleboy/crosswalk,Pluto-tv/crosswalk,zeropool/crosswalk,tedshroyer/crosswalk,alex-zhang/crosswalk,stonegithubs/crosswalk,DonnaWuDongxia/crosswalk,hgl888/crosswalk,Bysmyyr/crosswalk,tomatell/crosswalk,axinging/crosswalk,amaniak/crosswalk,bestwpw/crosswalk,myroot/crosswalk,myroot/crosswalk,hgl888/crosswalk,qjia7/crosswalk,axinging/crosswalk,ZhengXinCN/crosswalk,jondwillis/crosswalk,heke123/crosswalk,axinging/crosswalk,qjia7/crosswalk,hgl888/crosswalk-efl,PeterWangIntel/crosswalk,amaniak/crosswalk,hgl888/crosswalk-efl,rakuco/crosswalk,xzhan96/crosswalk,dreamsxin/crosswalk,crosswalk-project/crosswalk-efl,mrunalk/crosswalk,lincsoon/crosswalk,huningxin/crosswalk,PeterWangIntel/crosswalk,hgl888/crosswalk,chuan9/crosswalk,crosswalk-project/crosswalk-efl,lincsoon/crosswalk,darktears/crosswalk,leonhsl/crosswalk,jondwillis/crosswalk,lincsoon/crosswalk,crosswalk-project/crosswalk-efl,qjia7/crosswalk,TheDirtyCalvinist/spacewalk,ZhengXinCN/crosswalk,ZhengXinCN/crosswalk,bestwpw/crosswalk,zliang7/crosswalk,ZhengXinCN/crosswalk,dreamsxin/crosswalk,PeterWangIntel/crosswalk,Pluto-tv/crosswalk,heke123/crosswalk,zeropool/crosswalk,jpike88/crosswalk,zliang7/crosswalk,myroot/crosswalk,crosswalk-project/crosswalk-efl,marcuspridham/crosswalk,crosswalk-project/crosswalk-efl,crosswalk-project/crosswalk,heke123/crosswalk,jpike88/crosswalk,marcuspridham/crosswalk,stonegithubs/crosswalk,siovene/crosswalk,jpike88/crosswalk,fujunwei/crosswalk,hgl888/crosswalk-efl,fujunwei/crosswalk,TheDirtyCalvinist/spacewalk,zliang7/crosswalk,darktears/crosswalk,baleboy/crosswalk,huningxin/crosswalk,rakuco/crosswalk,xzhan96/crosswalk,siovene/crosswalk,PeterWangIntel/crosswalk,weiyirong/crosswalk-1,jpike88/crosswalk,crosswalk-project/crosswalk,ZhengXinCN/crosswalk,hgl888/crosswalk-efl,tedshroyer/crosswalk,minggangw/crosswalk,pk-sam/crosswalk,leonhsl/crosswalk,amaniak/crosswalk,weiyirong/crosswalk-1,darktears/crosswalk,chuan9/crosswalk,leonhsl/crosswalk,axinging/crosswalk