Prevent crash when trying to dismiss an already dismissed infobar.

chrome/browser/ui/auto_login_info_bar_delegate.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 "chrome/browser/ui/auto_login_info_bar_delegate.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
 #include "base/metrics/histogram.h"
@@ skipping 204 matching lines @@
 }
 
 void AutoLoginInfoBarDelegate::RecordHistogramAction(int action) {
   UMA_HISTOGRAM_ENUMERATION("AutoLogin.Regular", action, HISTOGRAM_MAX);
 }
 
 void AutoLoginInfoBarDelegate::Observe(int type,
                                        const NotificationSource& source,
                                        const NotificationDetails& details) {
   DCHECK_EQ(chrome::NOTIFICATION_GOOGLE_SIGNED_OUT, type);
-  owner()->RemoveInfoBar(this);
+  // owner() can be NULL when InfoBarTabHelper removes us. See
+  // |InfoBarDelegate::clear_owner|.
+  if (owner())
+    owner()->RemoveInfoBar(this);
 }