Add kInvisible AX state to AnnounceTextView.

This ensures that the AnnounceTextView is purely an announcement and
cannot be navigated to by a screen reader.

reader.

Bug: 1161047, 1055150
Change-Id: I6ca8157261b2f8fc94978121807de008d59166d4
AX-Relnotes: Announcements in Views are not navigable to by a screen
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2617220Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Abigail Klein <abigailbklein@google.com>
Cr-Commit-Position: refs/heads/master@{#842100}

ui/views/widget/root_view.cc

@@ -76,6 +76,7 @@ class AnnounceTextView : public View {
     // May require setting kLiveStatus, kContainerLiveStatus to "polite".
     node_data->role = ax::mojom::Role::kAlert;
     node_data->SetName(announce_text_);
+    node_data->AddState(ax::mojom::State::kInvisible);
   }
 
  private: