[Extensions] Don't allow built-in extensions code to be overridden

extensions/renderer/resources/messaging.js

Index: extensions/renderer/resources/messaging.js
diff --git a/extensions/renderer/resources/messaging.js b/extensions/renderer/resources/messaging.js
index 5fe9920588a2315b8087d3af7d5e404ff8995b48..5a7ec1e40dc01d492c542729ddaacbd9def8b323 100644
--- a/extensions/renderer/resources/messaging.js
+++ b/extensions/renderer/resources/messaging.js
@@ -377,16 +377,16 @@ var Port = utils.expose('Port', PortImpl, { functions: [
     'onMessage'
   ] });
 
-exports.kRequestChannel = kRequestChannel;
-exports.kMessageChannel = kMessageChannel;
-exports.kNativeMessageChannel = kNativeMessageChannel;
-exports.Port = Port;
-exports.createPort = createPort;
-exports.sendMessageImpl = sendMessageImpl;
-exports.sendMessageUpdateArguments = sendMessageUpdateArguments;
+exports.$set('kRequestChannel', kRequestChannel);
+exports.$set('kMessageChannel', kMessageChannel);
+exports.$set('kNativeMessageChannel', kNativeMessageChannel);
+exports.$set('Port', Port);
+exports.$set('createPort', createPort);
+exports.$set('sendMessageImpl', sendMessageImpl);
+exports.$set('sendMessageUpdateArguments', sendMessageUpdateArguments);
 
 // For C++ code to call.
-exports.hasPort = hasPort;
-exports.dispatchOnConnect = dispatchOnConnect;
-exports.dispatchOnDisconnect = dispatchOnDisconnect;
-exports.dispatchOnMessage = dispatchOnMessage;
+exports.$set('hasPort', hasPort);
+exports.$set('dispatchOnConnect', dispatchOnConnect);
+exports.$set('dispatchOnDisconnect', dispatchOnDisconnect);
+exports.$set('dispatchOnMessage', dispatchOnMessage);