Fix interstitial pages not updating the task manager renderers' titles and favicons

chrome/browser/task_management/providers/web_contents/guest_task.cc

 // Copyright 2015 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/task_management/providers/web_contents/guest_task.h"
 
 #include "components/guest_view/browser/guest_view_base.h"
 #include "content/public/browser/web_contents.h"
 #include "ui/base/l10n/l10n_util.h"
 
@@ skipping 22 matching lines @@
   return Task::GUEST;
 }
 
 base::string16 GuestTask::GetCurrentTitle(
     content::WebContents* web_contents) const {
   DCHECK(web_contents);
 
   guest_view::GuestViewBase* guest =
       guest_view::GuestViewBase::FromWebContents(web_contents);
 
-  DCHECK(guest);
+  if (!guest) {
+    // This can happen when an AppWindowContentsImpl is destroyed. It emits a
+    // DidFinishNavigation() events to the WebContentsObservers which triggers a
+    // title update in WebContentsTaskProvider. This happens before
+    // WebContentsDestroyed() is emitted.
+    return title();
+  }
 
   base::string16 title =
       l10n_util::GetStringFUTF16(guest->GetTaskPrefix(),
                                  RendererTask::GetTitleFromWebContents(
                                      web_contents));
 
   return title;
 }
 
 }  // namespace task_management