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 61270fef278a22646c24cd5fa97d188e32dabd2d..e31bf652b582bb1419dd37971b93ea24fdc6a95e 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;
 };