Added more typechecking functions and unit tests for existing code.

remoting/webapp/crd/js/video_frame_recorder.js

Index: remoting/webapp/crd/js/video_frame_recorder.js
diff --git a/remoting/webapp/crd/js/video_frame_recorder.js b/remoting/webapp/crd/js/video_frame_recorder.js
index 25150699aa922eefd00789b0654004476e6718a7..a5bceb91029c4f8e365325ab4768a1e2df60de4e 100644
--- a/remoting/webapp/crd/js/video_frame_recorder.js
+++ b/remoting/webapp/crd/js/video_frame_recorder.js
@@ -63,8 +63,8 @@ remoting.VideoFrameRecorder.prototype.handleMessage =
     return false;
   }
 
-  var messageType = getStringAttr(message, 'type');
-  var messageData = getStringAttr(message, 'data');
+  var messageType = base.getStringAttr(message, 'type');
+  var messageData = base.getStringAttr(message, 'data');
 
   if (messageType == 'next-frame-reply') {
     if (!this.fileWriter_) {