Tab scrolling not working

[Citron, David]

Scrolling tabs in the "tabs" feature was not working for me.

The issue appears to be that the event handler registration is
incorrect?

  leftNav.onclick = function(event) {
    this.smoothScroll_(wrapper, -120);
  };
  rightNav.onclick = function(event) {
    this.smoothScroll_(wrapper, 120);
  };

The "this" pointer at the time the event fires is referring to the
HTMLElement object, not the TabSet object.

I created https://issues.apache.org/jira/browse/SHINDIG-667 with a patch
that worked for me.

Thanks,
Dave