You Can use button object in which inside action tab you can add action as Maximize Object. In this action you need to pass object id of your chart so that once you click on the button the chart will be maximized.
Is this your requirement?
Also you can use If condtion in general tab of button to execute this action.
Your users could just right click the Object and then click Maximise, Restore or Minimise as per their wont.
This saves screen real estate by not cluttering your dashboard up with buttons. It won't take long for your users to get used this and then learn that they can do this on any Object, plus they can also use Send to Excel.
Or you can put the icons on the Caption line.
Best Regards, Bill