fix #525 and #540, inline event handler will not be patched with zone. And when you want to get the inline event handler will return null.

<button id="btn1" onclick="func()">ok</button>

The func will not be patched, and if you access document.getElementById('btn1').onclick will return null.

The PR will not totally fixed the issue, if you don't access the elem.onclick for example, still no patch(but not null, you will get the original native version handler). you should add the following code to patch if you want to handle inline event handler

          var all = document.getElementsByTagName("*");

          for (var i=0, max=all.length; i < max; i++) {
           var elem = all[i];
           for (var j = 0; j < eventNames.length; j ++) {
             var attr = eventNames[j];
             var attrValue = elem['on' + attr];
           }
          }