I got it working on Chrome by executing webvi_init() on s.onload():

  javascript:(function(){var d=document;var t=d.getElementsByTagName('textarea');for(var i in t){if(typeof t[i]=='object') t[i].setAttribute('class','webvi');} var s=d.createElement('script');s.setAttribute('src','http://webvi.googlecode.com/svn/trunk/lib/webvi.js');d.body.appendChild(s);s.onload=function(){webvi_init();};})();