fix a layout test crash due to no browser window

content/shell/browser/layout_test/layout_test_download_manager_delegate.cc

Index: content/shell/browser/layout_test/layout_test_download_manager_delegate.cc
diff --git a/content/shell/browser/layout_test/layout_test_download_manager_delegate.cc b/content/shell/browser/layout_test/layout_test_download_manager_delegate.cc
index 9f7b098b622bfa343e648f9ac7410e6f517e2925..9516f096dce376b494e30700794b997c58bc6d15 100644
--- a/content/shell/browser/layout_test/layout_test_download_manager_delegate.cc
+++ b/content/shell/browser/layout_test/layout_test_download_manager_delegate.cc
@@ -35,7 +35,8 @@ 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()));