Add dummy implementations for TrayIcon.

atom/browser/ui/tray_icon_cocoa.mm

@@ -0,0 +1,24 @@
+// 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.
+
+#include "atom/browser/ui/tray_icon_cocoa.h"
+
+namespace atom {
+
+TrayIconCocoa::TrayIconCocoa() {
+}
+
+TrayIconCocoa::~TrayIconCocoa() {
+}
+
+void TrayIconCocoa::SetImage(const gfx::ImageSkia& image) {
+}
+
+void TrayIconCocoa::SetPressedImage(const gfx::ImageSkia& image) {
+}
+
+void TrayIconCocoa::SetToolTip(const std::string& tool_tip) {
+}
+
+}  // namespace atom