Introduce 'grab_inputs' property for athena container.

athena/screen/public/screen_manager.h

Index: athena/screen/public/screen_manager.h
diff --git a/athena/screen/public/screen_manager.h b/athena/screen/public/screen_manager.h
index 9e873061d354d15815392a2dbd6b9c95d1090cd1..8a82f6c617272a0b59d7d527e61894dd5d3fcd4a 100644
--- a/athena/screen/public/screen_manager.h
+++ b/athena/screen/public/screen_manager.h
@@ -35,6 +35,9 @@ class ATHENA_EXPORT ScreenManager {
     // True if the container can activate its child window.
     bool can_activate_children;
 
+    // True if the container will grab all of input events.
+    bool grab_inputs;
+
     // Defines the z_order priority of the container.
     int z_order_priority;
   };