mus: Disregard windows that explicitly set can_accept_events to be false when sending events.

services/ui/public/interfaces/window_tree.mojom

Index: services/ui/public/interfaces/window_tree.mojom
diff --git a/services/ui/public/interfaces/window_tree.mojom b/services/ui/public/interfaces/window_tree.mojom
index 6440e2a6b0bd6038f588e259024d0d250888ef18..65416a8f11a6e8c3366d75dd359020292e505ba9 100644
--- a/services/ui/public/interfaces/window_tree.mojom
+++ b/services/ui/public/interfaces/window_tree.mojom
@@ -238,6 +238,10 @@ interface WindowTree {
   // Otherwise the existing state is used.
   SetImeVisibility(uint32 window_id, bool visible, mojo.TextInputState? state);
 
+  // Set whether the specified window can accept events. If a window does not
+  // accept events, none of its descendant windows accept events either.
+  SetCanAcceptEvents(uint32 window_id, bool accept_events);
+
   // See documentation for WindowTreeClient::OnWindowInputEvent().
   OnWindowInputEventAck(uint32 event_id, EventResult result);