Add "click" event for TrayIcon.

atom/browser/ui/tray_icon_observer.h

@@ -0,0 +1,20 @@
+// Copyright (c) 2014 GitHub, Inc. All rights reserved.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef ATOM_BROWSER_UI_TRAY_ICON_OBSERVER_H_
+#define ATOM_BROWSER_UI_TRAY_ICON_OBSERVER_H_
+
+namespace atom {
+
+class TrayIconObserver {
+ public:
+  virtual void OnClicked() {};
+
+ protected:
+  virtual ~TrayIconObserver() {};
+};
+
+}  // namespace atom
+
+#endif  // ATOM_BROWSER_UI_TRAY_ICON_OBSERVER_H_