[MIX-DL] Make notification announce itself to screen readers.

This CL is a small change to announce the arrival of a MIX-DL alert to
accessibility devices.

We don't have testing infrastructure for accessibility in the downloads
shelf right now, and this is a trivial change, so it's submitted without
tests. I manually verified that this works as expected on Mac OS.

Fixed: 1131084
Change-Id: Ie68a4f6ed5f71a25553deb2a776a7dcd3adf30a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2606669Reviewed-by: Xing Liu <xingliu@chromium.org>
Commit-Queue: Joe DeBlasio <jdeblasio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840772}

chrome/app/generated_resources.grd

@@ -2053,6 +2053,20 @@ are declared in tools/grit/grit_rule.gni.
                desc="The title of a download notification inidcating that the file may be malicious, and the Advanced Protection Program recommends sending the file to Google. This message is for screen reader users">
         <ph name="FILE_NAME">$1<ex>file.exe</ex></ph> is being scanned.
       </message>
+      <if expr="is_macosx">
+        <then>
+          <message name="IDS_PROMPT_DOWNLOAD_MIXED_CONTENT_BLOCKED_ACCESSIBLE_ALERT"
+                   desc="The title of a download notification inidcating that the download was delivered insecurely. This message is for screen reader users">
+            <ph name="FILE_NAME">$1<ex>file.exe</ex></ph> can't be downloaded securely.
+          </message>
+        </then>
+        <else>
+          <message name="IDS_PROMPT_DOWNLOAD_MIXED_CONTENT_BLOCKED_ACCESSIBLE_ALERT"
+                   desc="The title of a download notification inidcating that the download was delivered insecurely. This message is for screen reader users">
+            <ph name="FILE_NAME">$1<ex>file.exe</ex></ph> can't be downloaded securely. Press Shift+F6 to cycle to the downloads bar area.
+          </message>
+        </else>
+      </if>
 
       <!-- Download Notification Labels -->
       <message name="IDS_DOWNLOAD_NOTIFICATION_COPY_TO_CLIPBOARD"

chrome/app/generated_resources_grd/IDS_PROMPT_DOWNLOAD_MIXED_CONTENT_BLOCKED_ACCESSIBLE_ALERT.png.sha1

+5a7ce03653dab66e283e8303fa279a44ea171a81
\ No newline at end of file

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

@@ -696,6 +696,11 @@ void DownloadItemView::UpdateMode(Mode mode) {
       UpdateAccessibleAlert(model_->GetWarningText(unelided_filename, &ignore));
       accessible_alert_timer_.Stop();
     }
+  } else if (is_mixed_content(mode_)) {
+    announce_accessible_alert_soon_ = true;
+    UpdateAccessibleAlert(l10n_util::GetStringFUTF16(
+        IDS_PROMPT_DOWNLOAD_MIXED_CONTENT_BLOCKED_ACCESSIBLE_ALERT,
+        unelided_filename));
   } else if (mode_ == Mode::kDeepScanning) {
     UpdateAccessibleAlert(l10n_util::GetStringFUTF16(
         IDS_DEEP_SCANNING_ACCESSIBLE_ALERT, unelided_filename));