Disable off-store extension installs by default.

chrome/browser/download/download_shelf_context_menu.cc

Index: chrome/browser/download/download_shelf_context_menu.cc
diff --git a/chrome/browser/download/download_shelf_context_menu.cc b/chrome/browser/download/download_shelf_context_menu.cc
index ddc9c9d8f4364968466ae018182f766a9a287df9..d4a90d4d83ef4f79b60e8314db966440b0813984 100644
--- a/chrome/browser/download/download_shelf_context_menu.cc
+++ b/chrome/browser/download/download_shelf_context_menu.cc
@@ -8,6 +8,7 @@
 #include "chrome/browser/download/download_crx_util.h"
 #include "chrome/browser/download/download_item_model.h"
 #include "chrome/browser/download/download_prefs.h"
+#include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/safe_browsing/download_protection_service.h"
 #include "chrome/browser/safe_browsing/safe_browsing_service.h"
 #include "chrome/common/extensions/extension.h"
@@ -46,11 +47,15 @@ bool DownloadShelfContextMenu::IsCommandIdEnabled(int command_id) const {
     case SHOW_IN_FOLDER:
       return download_item_->CanShowInFolder() &&
           !download_item_->IsTemporary();
-    case OPEN_WHEN_COMPLETE:
+    case OPEN_WHEN_COMPLETE: {
+      Profile* profile =
+          Profile::FromBrowserContext(download_item_->GetBrowserContext());
       return download_item_->CanShowInFolder() &&
           !download_item_->IsTemporary() &&
           (!Extension::IsExtension(download_item_->GetTargetName()) ||
-           download_crx_util::ShouldOpenExtensionDownload(*download_item_));
+           download_crx_util::ShouldOpenExtensionDownload(
+               profile->GetExtensionService(), *download_item_));
+    }
     case ALWAYS_OPEN_TYPE:
       // For temporary downloads, the target filename might be a temporary
       // filename. Don't base an "Always open" decision based on it. Also