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

chrome/browser/ui/cocoa/profiles/user_manager_mac.h

 // Copyright 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_COCOA_PROFILES_USER_MANAGER_MAC_H_
 #define CHROME_BROWSER_UI_COCOA_PROFILES_USER_MANAGER_MAC_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/mac/scoped_nsobject.h"
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_window.h"
 
 @class UserManagerWindowController;
 
 namespace content {
 class NavigationController;
 class WebContents;
 }
 
-// Dialog widget that contains the Desktop User Manager webui.
+// Dialog widget that contains the Desktop User Manager webui. This object
+// should always be created from the UserManager::Show() method. Note that only
+// one User Manager will exist at a time.
 class UserManagerMac {
  public:
-  // Shows the User Manager or re-activates an existing one, focusing the
-  // profile given by |profile_path_to_focus|. Based on the value of
-  // |tutorial_mode|, a tutorial could be shown, in which case
-  // |profile_path_to_focus| is ignored.
-  static void Show(const base::FilePath& profile_path_to_focus,
-                   profiles::UserManagerTutorialMode tutorial_mode);
-
-  // Hide the User Manager.
-  static void Hide();
-
-  // Returns whether or not the User Manager is showing.
-  static bool IsShowing();
-
   // Called by the cocoa window controller when its window closes and the
   // controller destroyed itself. Deletes the instance.
   void WindowWasClosed();
 
+  // Called from the UserManager class once the |guest_profile| is ready. Will
+  // construct a UserManagerMac object and show |url|.
+  static void OnGuestProfileCreated(Profile* guest_profile,
+                                    const std::string& url);
+
+  UserManagerWindowController* window_controller() {
+    return window_controller_.get();
+  }
+
  private:
   explicit UserManagerMac(Profile* profile);
   virtual ~UserManagerMac();
 
-  // Creates a new UserManagerMac instance for the |guest_profile| and
-  // shows the |url|.
-  static void OnGuestProfileCreated(Profile* guest_profile,
-                                    const std::string& url);
-
-  // An open User Manager window. There can only be one open at a time. This
-  // is reset to NULL when the window is closed.
-  static UserManagerMac* instance_;  // Weak.
-
   // Controller of the window.
   base::scoped_nsobject<UserManagerWindowController> window_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(UserManagerMac);
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_PROFILES_USER_MANAGER_MAC_H_