- 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.cc
#include "atom/browser/ui/tray_icon.h"
namespace atom {
TrayIcon::TrayIcon() {
}
TrayIcon::~TrayIcon() {
}
void TrayIcon::SetPressedImage(ImageType image) {
}
void TrayIcon::SetTitle(const std::string& title) {
}
void TrayIcon::SetHighlightMode(TrayIcon::HighlightMode mode) {
}
void TrayIcon::DisplayBalloon(ImageType icon,