- Electron version:1.3.3
- Operating system:win10/mac

the Tray instance events shold provide the tray hover event. 
`tray.setToolTip` has limitations when do more operation.

atom/browser/ui/tray_icon.h
void RemoveObserver(TrayIconObserver* obs) { observers_.RemoveObserver(obs); }
  void NotifyClicked(const gfx::Rect& = gfx::Rect(), int modifiers = 0);
  void NotifyDoubleClicked(const gfx::Rect& = gfx::Rect(), int modifiers = 0);
  void NotifyBalloonShow();
  void NotifyBalloonClicked();
  void NotifyBalloonClosed();
  void NotifyRightClicked(const gfx::Rect& bounds = gfx::Rect(),
                          int modifiers = 0);
  void NotifyDrop();
  void NotifyDropFiles(const std::vector<std::string>& files);
  void NotifyDropText(const std::string& text);
  void NotifyDragEntered();
  void NotifyDragExited();
  void NotifyDragEnded();
 protected:
  TrayIcon();
 private:
  base::ObserverList<TrayIconObserver> observers_;
  DISALLOW_COPY_AND_ASSIGN(TrayIcon);
};
}  
#endif