Access to Chrome via the System Tray should go through the User Manager.

chrome/browser/ui/user_manager.h

Index: chrome/browser/ui/user_manager.h
diff --git a/chrome/browser/ui/user_manager.h b/chrome/browser/ui/user_manager.h
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+// Copyright (c) 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_UI_USER_MANAGER_H_
+#define CHROME_BROWSER_UI_USER_MANAGER_H_
+
+#include "chrome/browser/profiles/profile_window.h"
+
+namespace base {
+class FilePath;
+}
+
+// Cross-platform methods for displaying the user manager.
+class UserManager {
+ public:
+  // Shows the User Manager or re-activates an existing one, focusing the
+  // profile given by |profile_path_to_focus|; passing an empty base::FilePath
+  // focuses no user pod. Based on the value of |tutorial_mode|, a tutorial
+  // could be shown, in which case |profile_path_to_focus| is ignored. After a
+  // profile is opened, executes the |profile_open_action|.
+  static void Show(const base::FilePath& profile_path_to_focus,
+                   profiles::UserManagerTutorialMode tutorial_mode,
+                   profiles::UserManagerProfileSelected profile_open_action);
+
+  // Hides the User Manager.
+  static void Hide();
+
+  // Returns whether the User Manager is showing.
+  static bool IsShowing();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(UserManager);
+};
+
+#endif  // CHROME_BROWSER_UI_USER_MANAGER_H_