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

chrome/browser/download/download_crx_util.cc

Index: chrome/browser/download/download_crx_util.cc
diff --git a/chrome/browser/download/download_crx_util.cc b/chrome/browser/download/download_crx_util.cc
index ab242df7db48414c59601f0ceb58e31186fe7d45..4a2d8ac208854ac8890b3700f0c7cd19218a792a 100644
--- a/chrome/browser/download/download_crx_util.cc
+++ b/chrome/browser/download/download_crx_util.cc
@@ -11,6 +11,7 @@
 #include "chrome/browser/extensions/webstore_installer.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/chrome_notification_types.h"
+#include "chrome/common/extensions/switch_utils.h"
 #include "content/public/browser/download_item.h"
 #include "content/public/browser/notification_service.h"
 
@@ -50,6 +51,15 @@ void SetMockInstallUIForTesting(ExtensionInstallUI* mock_ui) {
   mock_install_ui_for_testing = mock_ui;
 }
 
+bool ShouldOpenExtensionDownload(const DownloadItem& download_item) {
+  if (extensions::switch_utils::IsOffStoreInstallEnabled() ||
+      WebstoreInstaller::GetAssociatedApproval(download_item)) {
+    return true;
+  } else {
+    return false;
+  }
+}
+
 scoped_refptr<CrxInstaller> OpenChromeExtension(
     Profile* profile,
     const DownloadItem& download_item) {