- 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
#ifndef ATOM_BROWSER_UI_TRAY_ICON_H_
#define ATOM_BROWSER_UI_TRAY_ICON_H_
#include <string>
#include <vector>
#include "atom/browser/ui/atom_menu_model.h"
#include "atom/browser/ui/tray_icon_observer.h"
#include "base/observer_list.h"
#include "ui/gfx/geometry/rect.h"
namespace atom {
class TrayIcon {