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 145894)
+++ chrome/browser/ui/webui/signin/login_ui_service.h	(working copy)
@@ -7,6 +7,7 @@
 #pragma once
 
 #include "base/basictypes.h"
+#include "base/observer_list.h"
 #include "chrome/browser/profiles/profile_keyed_service.h"
 
 class Browser;
@@ -29,6 +30,21 @@
     virtual ~LoginUI() {}
   };
 
+  // Interface for obervers of LoginUIService.
+  class Observer {
+   public:
+    // Called when a new login UI is shown.
+    // |ui| The login UI that was just shown. Will never be null.
+    virtual void OnLoginUIShown(LoginUI* ui) = 0;
+
+    // Called when a login UI is closed.
+    // |ui| The login UI that was just closed; will never be null.
+    virtual void OnLoginUIClosed(LoginUI* ui) = 0;
+
+   protected:
+    virtual ~Observer() {}
+  };
+
   LoginUIService();
   virtual ~LoginUIService();
 
@@ -37,6 +53,10 @@
     return ui_;
   }
 
+  // |observer| The observer to add or remove; cannot be NULL.
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
   // Sets the currently active login UI. It is illegal to call this if there is
   // already login UI visible.
   void SetLoginUI(LoginUI* ui);
@@ -54,6 +74,9 @@
   // Weak pointer to the currently active login UI, or null if none.
   LoginUI* ui_;
 
+  // List of observers.
+  ObserverList<Observer> observer_list_;
+
   DISALLOW_COPY_AND_ASSIGN(LoginUIService);
 };