perform a null check in case WebContents doesn't have a ChromeDownloadDelegate

chrome/browser/android/download/download_controller.cc

 // Copyright 2016 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/android/download/download_controller.h"
 
 #include <memory>
 #include <utility>
 
 #include "base/android/context_utils.h"
@@ skipping 226 matching lines @@
 void DownloadController::OnDownloadStarted(
     DownloadItem* download_item) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   WebContents* web_contents = download_item->GetWebContents();
   if (!web_contents)
     return;
 
   // Register for updates to the DownloadItem.
   download_item->AddObserver(this);
 
-  ChromeDownloadDelegate::FromWebContents(web_contents)->OnDownloadStarted(
-      download_item->GetTargetFilePath().BaseName().value());
+  ChromeDownloadDelegate* delegate =
+      ChromeDownloadDelegate::FromWebContents(web_contents);
+  if (delegate) {
+    delegate->OnDownloadStarted(
+        download_item->GetTargetFilePath().BaseName().value());
+  }
 }
 
 void DownloadController::OnDownloadUpdated(DownloadItem* item) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   if (item->IsDangerous() && (item->GetState() != DownloadItem::CANCELLED))
     OnDangerousDownload(item);
 
   JNIEnv* env = base::android::AttachCurrentThread();
   ScopedJavaLocalRef<jstring> jguid =
       ConvertUTF8ToJavaString(env, item->GetGuid());
@@ skipping 108 matching lines @@
   if (!item)
     return;
   if (accept) {
     item->ValidateDangerousDownload();
   } else {
     DownloadController::RecordDownloadCancelReason(
         DownloadController::CANCEL_REASON_DANGEROUS_DOWNLOAD_INFOBAR_DISMISSED);
     item->Remove();
   }
 }