old_contents: <MDL.Tooltip 
  					element = {<i className="material-icons">add</i>}
  					text = 'Follow'
  					large = {true}
  					style = {tooltipStyle}
  />
  <MDL.Tooltip 
  					element = 'Please move your mouse on it.'
  					text = 'this is a bird.'
  					url = 'https://dl.dropboxusercontent.com/u/107164257/CSS3Images/CSS3/bird.png'
  					large = {true}
  					width = {30}
  					height = {30}
  					style = {tooltipStyle}
  				/>
new_contents: <Tooltip 
  					element = {<i className="material-icons">add</i>}
  					text = 'Follow'
  					large = {true}
  					style = {tooltipStyle}
  />
  <Tooltip 
  					element = 'Please move your mouse on it.'
  					text = 'this is a bird.'
  					url = 'https://dl.dropboxusercontent.com/u/107164257/CSS3Images/CSS3/bird.png'
  					large = {true}
  					width = {30}
  					height = {30}
  					style = {tooltipStyle}
  				/>
subject: 修改tooltip.js