Add a method to LoginUIService to open the sign in UI in a popup.

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

Index: chrome/browser/ui/webui/signin/login_ui_service.h
===================================================================
--- chrome/browser/ui/webui/signin/login_ui_service.h	(revision 144917)
+++ chrome/browser/ui/webui/signin/login_ui_service.h	(working copy)
@@ -39,10 +39,12 @@
 
   // Sets the currently active login UI. It is illegal to call this if there is
   // already login UI visible.
+  // Fires chrome::NOTIFICATION_LOGIN_UI_CHANGED.
   void SetLoginUI(LoginUI* ui);
 
   // Called when login UI is closed. If the passed UI is the current login UI,
   // sets current_login_ui() to null.
+  // Fires chrome::NOTIFICATION_LOGIN_UI_CHANGED.
   void LoginUIClosed(LoginUI* ui);
 
   // Brings the login UI to the foreground, or if there is no login UI,
@@ -50,7 +52,15 @@
   // Virtual for mocking purposes.
   virtual void ShowLoginUI(Browser* browser);
 
+  // Same as ShowLoginUI but opens a popup with the login UI instead of a
+  // new tab.
+  // Note that if an existing login UI is already open, this method will focus
+  // that UI even though it is not a popup.
+  virtual void ShowLoginDialogUI(Browser* browser);
+
  private:
+  void FireLoginUIChanged() const;
+
   // Weak pointer to the currently active login UI, or null if none.
   LoginUI* ui_;