[Presentation API] (alternative) 1-UA: send message between controller and receiver page

extensions/renderer/resources/media_router_bindings.js

Index: extensions/renderer/resources/media_router_bindings.js
diff --git a/extensions/renderer/resources/media_router_bindings.js b/extensions/renderer/resources/media_router_bindings.js
index 5f0d9a0a824f59254b49332b6eb0c2b39469bccf..3d73668d5aa3a7d9bc7a3700d44750dc7f7ff9ba 100644
--- a/extensions/renderer/resources/media_router_bindings.js
+++ b/extensions/renderer/resources/media_router_bindings.js
@@ -80,7 +80,8 @@ define('media_router_bindings', [
       // Begin newly added properties, followed by the milestone they were
       // added.  The guard should be safe to remove N+2 milestones later.
       'for_display': route.forDisplay, // M47
-      'incognito': !!route.offTheRecord  // M50
+      'incognito': !!route.offTheRecord,  // M50
+      'is_offscreen_presentation': !!route.isOffscreenPresentation // M56
     });
   }