Start moving signin code out of browser/sync.

chrome/browser/ui/webui/signin/login_ui_service.h

+// Copyright (c) 2012 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_WEBUI_SIGNIN_LOGIN_UI_SERVICE_H_
+#define CHROME_BROWSER_UI_WEBUI_SIGNIN_LOGIN_UI_SERVICE_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "chrome/browser/profiles/profile_keyed_service.h"
+
+class Profile;
+
+namespace content {
+class WebUI;
+};
+
+// The LoginUIService helps track per-profile information for the login UI -
+// for example, whether there is login UI currently on-screen.
+class LoginUIService : public ProfileKeyedService {

[tim (not reviewing), 2012/02/14 17:22:29]

So this class isn't meant to be used on all platforms/embeddings, correct?  Can
you add a comment explaining where the bypasses might happen?

[Andrew T Wilson (Slow), 2012/02/14 20:52:36]

I'm not sure what you mean. Can you clarify? This class basically just keeps
track of the current login screen, because our current login UI flow enforces
having only a single login screen visible, so trying to bring up login UI should
pop up the existing UI if one is visible.

+ public:
+  // Creates a LoginUIService associated with the passed |profile|. |profile|
+  // is used to create a new browser in the case that ShowLoginUI() is invoked
+  // when no browser windows are open (e.g. via the Mac menu bar).
+  explicit LoginUIService(Profile* profile);
+  virtual ~LoginUIService();
+
+  // Gets the currently active login UI, or null if no login UI is active.
+  content::WebUI* current_login_ui() const {
+    return ui_;
+  }
+
+  // Sets the currently active login UI. It is illegal to call this if there is
+  // already login UI visible.
+  void SetLoginUI(content::WebUI* ui);
+
+  // If the passed UI is the current login UI, resets it (called when login UI
+  // is being shut down).
+  void ResetLoginUI(content::WebUI* ui);

[tim (not reviewing), 2012/02/14 17:22:29]

I'm substantially confused about the difference between Set and Reset here.  I
think in your comment 'resets it' implies 'sets it to NULL', but in the
function, 'Reset' can imply 'Change to other ui*'?  

[Andrew T Wilson (Slow), 2012/02/14 20:52:36]

Sigh, this used to be ClearLoginUI(), but jhawkins asked me to change it (and I
agree with his reasoning). I'm going to change this to LoginUIClosed() instead
which I hope addresses everyone's concerns.

+
+  // Brings the current login UI for this profile to the foreground (it is an
+  // error to call this if there is no visible login UI.
+  void FocusLoginUI();
+
+  // Displays the login dialog to the user.
+  void ShowLoginUI();
+
+ private:
+  // Weak pointer to the currently active login UI, or null if none.
+  content::WebUI* ui_;
+
+  // Weak pointer to the profile this service is associated with.
+  Profile* profile_;
+
+  DISALLOW_COPY_AND_ASSIGN(LoginUIService);
+};
+
+
+#endif  // CHROME_BROWSER_UI_WEBUI_SIGNIN_LOGIN_UI_SERVICE_H_