Google Chart Gannt 避免工具提示

google.charts.load('current', {
  packages:['gantt']
}).then(function () {
  var data = new google.visualization.DataTable();
  data.addColumn('string', 'Task ID');
  data.addColumn('string', 'Task Name');
  data.addColumn('date', 'Start Date');
  data.addColumn('date', 'End Date');
  data.addColumn('number', 'Duration');
  data.addColumn('number', 'Percent Complete');
  data.addColumn('string', 'Dependencies');

  data.addRows([
    ['Research', 'Find sources',
     new Date(2015, 0, 1), new Date(2015, 0, 5), null,  100,  null],
    ['Write', 'Write paper',
     null, new Date(2015, 0, 9), daysToMilliseconds(3), 25, 'Research,Outline'],
    ['Cite', 'Create bibliography',
     null, new Date(2015, 0, 7), daysToMilliseconds(1), 20, 'Research'],
    ['Complete', 'Hand in paper',
     null, new Date(2015, 0, 10), daysToMilliseconds(1), 0, 'Cite,Write'],
    ['Outline', 'Outline paper',
     null, new Date(2015, 0, 6), daysToMilliseconds(1), 100, 'Research']
  ]);

  var options = {
    height: 275
  };

  var container = document.getElementById('chart_div');
  var chart = new google.visualization.Gantt(container);

  google.visualization.events.addOneTimeListener(chart, 'ready', function () {
    var observer = new MutationObserver(function (nodes) {
      Array.prototype.forEach.call(nodes, function(node) {
        if (node.addedNodes.length > 0) {
          Array.prototype.forEach.call(node.addedNodes, function(addedNode) {
            if ((addedNode.tagName === 'rect') && (addedNode.getAttribute('fill') === 'white')) {
              addedNode.setAttribute('fill', 'transparent');
              addedNode.setAttribute('stroke', 'transparent');
              Array.prototype.forEach.call(addedNode.parentNode.getElementsByTagName('text'), function(label) {
                label.setAttribute('fill', 'transparent');
              });
            }
          });
        }
      });
    });
    observer.observe(container, {
      childList: true,
      subtree: true
    });
  });

  chart.draw(data, options);

  function daysToMilliseconds(days) {
    return days * 24 * 60 * 60 * 1000;
  }
});

<script src="https://www.gstatic.com/charts/loader.js"></script>
<div id="chart_div"></div>