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

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

Index: chrome/browser/task_management/providers/web_contents/guest_task.cc
diff --git a/chrome/browser/task_management/providers/web_contents/guest_task.cc b/chrome/browser/task_management/providers/web_contents/guest_task.cc
index bf092cbbe190a032b4adbc9781aa6b055fc6084c..7167c7d092b2ea50d54d1158f0c47228bbb3a1c4 100644
--- a/chrome/browser/task_management/providers/web_contents/guest_task.cc
+++ b/chrome/browser/task_management/providers/web_contents/guest_task.cc
@@ -40,7 +40,13 @@ base::string16 GuestTask::GetCurrentTitle(
   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(),