Add the --disable-off-store-extension-install switch.

chrome/browser/download/chrome_download_manager_delegate.cc

Index: chrome/browser/download/chrome_download_manager_delegate.cc
diff --git a/chrome/browser/download/chrome_download_manager_delegate.cc b/chrome/browser/download/chrome_download_manager_delegate.cc
index e069eddcbe8445310dd4b054cd0f2370aa27cdcd..5b2a0e97703a293f6d1697f4a4f1f2a791259e11 100644
--- a/chrome/browser/download/chrome_download_manager_delegate.cc
+++ b/chrome/browser/download/chrome_download_manager_delegate.cc
@@ -92,8 +92,12 @@ bool ChromeDownloadManagerDelegate::IsExtensionDownload(
   if (item->PromptUserForSaveLocation())
     return false;
 
-  return (item->GetMimeType() == Extension::kMimeType) ||
-      UserScript::IsURLUserScript(item->GetURL(), item->GetMimeType());
+  if ((item->GetMimeType() != Extension::kMimeType) &&
+      !UserScript::IsURLUserScript(item->GetURL(), item->GetMimeType())) {
+    return false;
+  }
+
+  return download_crx_util::ShouldOpenExtensionDownload(*item);
 }
 
 void ChromeDownloadManagerDelegate::SetDownloadManager(DownloadManager* dm) {