Add a Record button to the web-app if the host supports video recording.

remoting/webapp/client_screen.js

Index: remoting/webapp/client_screen.js
diff --git a/remoting/webapp/client_screen.js b/remoting/webapp/client_screen.js
index f1f0bac225af4c5576358136738ddaa35711fd47..b65383a451f0cdba75f11017b6adf7bf01d2d1d1 100644
--- a/remoting/webapp/client_screen.js
+++ b/remoting/webapp/client_screen.js
@@ -371,6 +371,9 @@ remoting.onConnected = function(clientSession) {
  * @return {boolean} Return true if the extension message was recognized.
  */
 remoting.onExtensionMessage = function(type, data) {
+  if (remoting.clientSession) {
+    return remoting.clientSession.handleExtensionMessage(type, data);
+  }
   return false;
 };