Don't create discard button when prompting for scanning

When prompting the user for APP scanning, the "Discard" button is still
present in the download shelf. It hidden behind the "Scan" button,
but still accessible via Tab/Enter keys, leading to accidental discards
when operating via keyboard.

This CL makes no visible changes to the UX.

Bug: 1049748
Change-Id: Ie4cb9fbc42341cca76bc5479e4ca9f207f7e9226
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2042388Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Commit-Queue: Daniel Rubery <drubery@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739147}

chrome/browser/ui/views/download/download_item_view.cc

@@ -1174,7 +1174,9 @@ void DownloadItemView::ShowWarningDialog() {
       model_->GetDangerType() !=
           download::DOWNLOAD_DANGER_TYPE_BLOCKED_TOO_LARGE &&
       model_->GetDangerType() !=
-          download::DOWNLOAD_DANGER_TYPE_SENSITIVE_CONTENT_BLOCK) {
+          download::DOWNLOAD_DANGER_TYPE_SENSITIVE_CONTENT_BLOCK &&
+      model_->GetDangerType() !=
+          download::DOWNLOAD_DANGER_TYPE_PROMPT_FOR_SCANNING) {
     auto discard_button = views::MdTextButton::Create(
         this, l10n_util::GetStringUTF16(IDS_DISCARD_DOWNLOAD));
     discard_button_ = AddChildView(std::move(discard_button));