fix a layout test crash due to no browser window

content/shell/browser/layout_test/layout_test_download_manager_delegate.cc

 // Copyright 2014 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 "content/shell/browser/layout_test/layout_test_download_manager_delegate.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
 #include <commdlg.h>
 #endif
@@ skipping 17 matching lines @@
 
 LayoutTestDownloadManagerDelegate::LayoutTestDownloadManagerDelegate()
     : ShellDownloadManagerDelegate() {}
 
 LayoutTestDownloadManagerDelegate::~LayoutTestDownloadManagerDelegate(){
 }
 
 bool LayoutTestDownloadManagerDelegate::ShouldOpenDownload(
       DownloadItem* item,
       const DownloadOpenDelayedCallback& callback) {
-  if (BlinkTestController::Get()->IsMainWindow(item->GetWebContents()) &&
+  if (BlinkTestController::Get() &&
+      BlinkTestController::Get()->IsMainWindow(item->GetWebContents()) &&
       item->GetMimeType() == "text/html") {
     BlinkTestController::Get()->OpenURL(
         net::FilePathToFileURL(item->GetFullPath()));
   }
   return true;
 }
 
 }  // namespace content