addEvent_(node, name, thisObject, func) {
    const event = Blockly.browserEvents.conditionalBind(
      node,
      name,
      thisObject,
      func,
    );
    this.boundEvents_.push(event);
  }
Helper method for adding an event.
@param {!Element} node Node upon which to listen.
@param {string} name Event name to listen to (e.g. 'mousedown').
@param {Object} thisObject The value of 'this' in the function.
@param {!Function} func Function to call when event is triggered.
@protected