Lock screen: ignore accelerator when system modal is open

Bug: 1011324
Change-Id: I4ae9d7cd8524ddfc294ea249d9992ad9a1a8b3c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2482263
Commit-Queue: Yunke Zhou <yunkez@google.com>
Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818463}

ash/login/ui/lock_contents_view.cc

@@ -2343,7 +2343,11 @@ void LockContentsView::PerformAction(LoginAcceleratorAction action) {
     ToggleSystemInfo();
     return;
   }
-  Shell::Get()->login_screen_controller()->HandleAccelerator(action);
+  // Do not allow accelerator action when system modal window is open except
+  // `kShowFeedback` which opens feedback tool on top of system modal.
+  if (!Shell::IsSystemModalWindowOpen() ||
+      action == LoginAcceleratorAction::kShowFeedback)
+    Shell::Get()->login_screen_controller()->HandleAccelerator(action);
 }
 
 bool LockContentsView::GetSystemInfoVisibility() const {