- 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/api/atom_api_tray.h
#ifndef ATOM_BROWSER_API_ATOM_API_TRAY_H_
#define ATOM_BROWSER_API_ATOM_API_TRAY_H_
#include <memory>
#include <string>
#include <vector>
#include "atom/browser/api/trackable_object.h"
#include "atom/browser/ui/tray_icon.h"
#include "atom/browser/ui/tray_icon_observer.h"
#include "native_mate/handle.h"
namespace gfx {
class Image;