- 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
#include "atom/browser/api/atom_api_tray.h"
#include <string>
#include "atom/browser/api/atom_api_menu.h"
#include "atom/browser/browser.h"
#include "atom/common/api/atom_api_native_image.h"
#include "atom/common/native_mate_converters/gfx_converter.h"
#include "atom/common/native_mate_converters/image_converter.h"
#include "atom/common/native_mate_converters/string16_converter.h"
#include "atom/common/node_includes.h"
#include "base/threading/thread_task_runner_handle.h"
#include "native_mate/constructor.h"
#include "native_mate/dictionary.h"
#include "ui/gfx/image/image.h"
namespace mate {
template<>
struct Converter<atom::TrayIcon::HighlightMode> {
  static bool FromV8(v8::Isolate* isolate, v8::Local<v8::Value> val,