Add user_info_ NULL check in case of guest mode.

ash/system/user/tray_user.cc

 // 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.
 
 #include "ash/system/user/tray_user.h"
 
 #include "ash/shell.h"
 #include "ash/system/tray/system_tray_delegate.h"
 #include "ash/system/tray/tray_constants.h"
 #include "ash/system/tray/tray_item_view.h"
@@ skipping 206 matching lines @@
     }
     return size;
   }
 
   virtual void Layout() OVERRIDE {
     views::View::Layout();
     if (bounds().IsEmpty())
       return;
 
     container_->SetBoundsRect(gfx::Rect(size()));
-    if (signout_) {
+    if (signout_ && user_info_) {
       gfx::Rect signout_bounds(signout_->GetPreferredSize());
       signout_bounds = bounds().Center(signout_bounds.size());
       signout_bounds.set_x(width() - signout_bounds.width() -
           kTrayPopupPaddingHorizontal);
       signout_->SetBoundsRect(signout_bounds);
 
       gfx::Rect usercard_bounds(user_info_->GetPreferredSize());
       usercard_bounds.set_width(signout_bounds.x());
       user_info_->SetBoundsRect(usercard_bounds);
-    } else {
+    } else if (signout_) {
+      signout_->SetBoundsRect(gfx::Rect(size()));
+    } else if (user_info_) {
       user_info_->SetBoundsRect(gfx::Rect(size()));
     }
   }
 
   user::LoginStatus login_;
 
   TrayPopupTextButtonContainer* container_;
   views::View* user_info_;
   views::Label* username_;
   views::Label* email_;
@@ skipping 58 matching lines @@
 }
 
 void TrayUser::OnUserUpdate() {
   avatar_->SetImage(
       ash::Shell::GetInstance()->tray_delegate()->GetUserImage(),
       gfx::Size(kUserIconSize, kUserIconSize));
 }
 
 }  // namespace internal
 }  // namespace ash