- 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_observer.h
#ifndef ATOM_BROWSER_UI_TRAY_ICON_OBSERVER_H_
#define ATOM_BROWSER_UI_TRAY_ICON_OBSERVER_H_
#include <string>
#include <vector>
namespace gfx {
class Rect;
}
namespace atom {
class TrayIconObserver {
 public:
  virtual void OnClicked(const gfx::Rect& bounds, int modifiers) {}
  virtual void OnDoubleClicked(const gfx::Rect& bounds, int modifiers) {}
  virtual void OnBalloonShow() {}
  virtual void OnBalloonClicked() {}
  virtual void OnBalloonClosed() {}
  virtual void OnRightClicked(const gfx::Rect& bounds, int modifiers) {}
  virtual void OnDrop() {}
  virtual void OnDropFiles(const std::vector<std::string>& files) {}
  virtual void OnDropText(const std::string& text) {}
  virtual void OnDragEntered() {}
  virtual void OnDragExited() {}
  virtual void OnDragEnded() {}
 protected:
  virtual ~TrayIconObserver() {}
};
}  
#endif