Improve the UI for disabling off-store extension install.

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 8711140c92acfaa549040c6963df0fe8bada1b1e..6b7c33dc05ec1a13e35c9e95fb3baa65373e8272 100644
--- a/chrome/browser/download/download_crx_util.cc
+++ b/chrome/browser/download/download_crx_util.cc
@@ -87,4 +87,17 @@ scoped_refptr<CrxInstaller> OpenChromeExtension(
   return installer;
 }
 
+bool IsExtensionDownload(const DownloadItem& download_item) {
+  if (download_item.PromptUserForSaveLocation())
+    return false;
+
+  if (download_item.GetMimeType() == extensions::Extension::kMimeType ||
+      UserScript::IsURLUserScript(download_item.GetURL(),
+                                  download_item.GetMimeType())) {
+    return true;
+  } else {
+    return false;
+  }
+}
+
 }  // namespace download_crx_util