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

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

 // 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.
 
 #include "chrome/browser/ui/cocoa/profiles/user_manager_mac.h"
 
 #include "chrome/app/chrome_command_ids.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/browser/ui/browser_dialogs.h"
 #import "chrome/browser/ui/cocoa/browser_window_utils.h"
 #include "chrome/browser/ui/cocoa/chrome_event_processing_window.h"
+#include "chrome/browser/ui/user_manager.h"
 #include "chrome/grit/chromium_strings.h"
 #include "content/public/browser/native_web_keyboard_event.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_delegate.h"
 #include "ui/base/l10n/l10n_util_mac.h"
 
 // Default window size. Taken from the views implementation in
 // chrome/browser/ui/views/user_manager_view.cc.
 // TODO(noms): Figure out if this size can be computed dynamically or adjusted
 // for smaller screens.
 const int kWindowWidth = 900;
 const int kWindowHeight = 700;
 
-namespace chrome {
-
-// Declared in browser_dialogs.h so others don't have to depend on this header.
-void ShowUserManager(const base::FilePath& profile_path_to_focus) {
-  UserManagerMac::Show(
-      profile_path_to_focus, profiles::USER_MANAGER_NO_TUTORIAL);
-}
-
-void ShowUserManagerWithTutorial(profiles::UserManagerTutorialMode tutorial) {
-  UserManagerMac::Show(base::FilePath(), tutorial);
-}
-
-void HideUserManager() {
-  UserManagerMac::Hide();
-}
-
-}  // namespace chrome
+// An open User Manager window. There can only be one open at a time. This
+// is reset to NULL when the window is closed.
+UserManagerMac* instance_ = NULL;  // Weak.

[Alexei Svitkine (slow), 2014/09/18 20:54:04]

Why not make it a static member of the class?

[Peter Kasting, 2014/09/18 21:33:47]

Being file-scoped in the .mm file is even more local than being static to the
class -- completely hides this implementation detail from readers of the header.

 
 // Custom WebContentsDelegate that allows handling of hotkeys.
 class UserManagerWebContentsDelegate : public content::WebContentsDelegate {
  public:
   UserManagerWebContentsDelegate(ChromeEventProcessingWindow* window)
     : window_(window) {}
 
   // WebContentsDelegate implementation. Forwards all unhandled keyboard events
   // to the current window.
   virtual void HandleKeyboardEvent(
@@ skipping 103 matching lines @@
 }
 
 - (void)windowWillClose:(NSNotification*)notification {
   [[NSNotificationCenter defaultCenter] removeObserver:self];
   DCHECK(userManagerObserver_);
   userManagerObserver_->WindowWasClosed();
 }
 
 @end
 
-// static
-UserManagerMac* UserManagerMac::instance_ = NULL;
 
-UserManagerMac::UserManagerMac(Profile* profile) {
-  window_controller_.reset([[UserManagerWindowController alloc]
-      initWithProfile:profile withObserver:this]);
-}
-
-UserManagerMac::~UserManagerMac() {
-}
-
-// static
-void UserManagerMac::Show(const base::FilePath& profile_path_to_focus,
-                          profiles::UserManagerTutorialMode tutorial_mode) {
+void UserManager::Show(
+    const base::FilePath& profile_path_to_focus,
+    profiles::UserManagerTutorialMode tutorial_mode,
+    profiles::UserManagerProfileSelected profile_open_action) {
   if (instance_) {
     // If there's a user manager window open already, just activate it.
-    [instance_->window_controller_ show];
+    [instance_->get_window_controller() show];
     return;
   }
 
   // Create the guest profile, if necessary, and open the User Manager
   // from the guest profile.
   profiles::CreateGuestProfileForUserManager(
       profile_path_to_focus,
       tutorial_mode,
+      profile_open_action,
       base::Bind(&UserManagerMac::OnGuestProfileCreated));
 }
 
-// static
-void UserManagerMac::Hide() {
+void UserManager::Hide() {
   if (instance_)
-    [instance_->window_controller_ close];
+    [instance_->get_window_controller() close];
 }
 
-// static
-bool UserManagerMac::IsShowing() {
-  return instance_ ? [instance_->window_controller_ isVisible]: false;
+bool UserManager::IsShowing() {
+  return instance_ ? [instance_->get_window_controller() isVisible]: false;
+}
+
+UserManagerMac::UserManagerMac(Profile* profile) {
+  window_controller_.reset([[UserManagerWindowController alloc]
+      initWithProfile:profile withObserver:this]);
+}
+
+UserManagerMac::~UserManagerMac() {
 }
 
 // static
 void UserManagerMac::OnGuestProfileCreated(Profile* guest_profile,
                                            const std::string& url) {
+  DCHECK(!instance_);
   instance_ = new UserManagerMac(guest_profile);
-  [instance_->window_controller_ showURL:GURL(url)];
+  [instance_->get_window_controller() showURL:GURL(url)];
 }
 
 void UserManagerMac::WindowWasClosed() {
   instance_ = NULL;
   delete this;
 }