Flag mouse messages received when cursor is hidden.

ui/platform_window/win/win_window.cc

Index: ui/platform_window/win/win_window.cc
diff --git a/ui/platform_window/win/win_window.cc b/ui/platform_window/win/win_window.cc
index f2830c16d7c516a5beff5a8e5c63553864c9d87a..745b7f71fc65dbc547207a035128866d389bec81 100644
--- a/ui/platform_window/win/win_window.cc
+++ b/ui/platform_window/win/win_window.cc
@@ -136,6 +136,8 @@ LRESULT WinWindow::OnMouseRange(UINT message, WPARAM w_param, LPARAM l_param) {
   std::unique_ptr<Event> event = EventFromNative(msg);
   if (IsMouseEventFromTouch(message))
     event->set_flags(event->flags() | EF_FROM_TOUCH);
+  if (IsWindowsCursorHidden())
+    event->set_flags(event->flags() | EF_CURSOR_HIDDEN);
   if (!(event->flags() & ui::EF_IS_NON_CLIENT))
     delegate_->DispatchEvent(event.get());
   SetMsgHandled(event->handled());