- 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.cc
tray_icon_->SetToolTip(tool_tip);
}
void Tray::SetTitle(const std::string& title) {
  tray_icon_->SetTitle(title);
}
void Tray::SetHighlightMode(TrayIcon::HighlightMode mode) {
  tray_icon_->SetHighlightMode(mode);
}
void Tray::DisplayBalloon(mate::Arguments* args,
                          const mate::Dictionary& options) {
  mate::Handle<NativeImage> icon;
  options.Get("icon", &icon);
  base::string16 title, content;
  if (!options.Get("title", &title) ||
      !options.Get("content", &content)) {
    args->ThrowError("'title' and 'content' must be defined");
    return;
  }
#if defined(OS_WIN)
  tray_icon_->DisplayBalloon(
      icon.IsEmpty() ? NULL : icon->GetHICON(GetSystemMetrics(SM_CXSMICON)),
      title, content);
#else
  tray_icon_->DisplayBalloon(
      icon.IsEmpty() ? gfx::Image() : icon->image(), title, content);
#endif
}
void Tray::PopUpContextMenu(mate::Arguments* args) {