Added more typechecking functions and unit tests for existing code.

remoting/webapp/crd/js/cast_extension_handler.js

Index: remoting/webapp/crd/js/cast_extension_handler.js
diff --git a/remoting/webapp/crd/js/cast_extension_handler.js b/remoting/webapp/crd/js/cast_extension_handler.js
index ab0bde22b41e3608392412a092c88e1763400bae..669a2b0ab76dd316aaee1e2e6909fff17feebb4b 100644
--- a/remoting/webapp/crd/js/cast_extension_handler.js
+++ b/remoting/webapp/crd/js/cast_extension_handler.js
@@ -93,7 +93,7 @@ remoting.CastExtensionHandler.prototype.start = function(sendMessageToHost) {
  * @param {string} msgString The extension message's data.
  */
 remoting.CastExtensionHandler.prototype.onMessage = function(msgString) {
-  var message = getJsonObjectFromString(msgString);
+  var message = base.getJsonObjectFromString(msgString);
 
   // Save messages to send after a session is established.
   this.messageQueue_.push(message);
@@ -243,7 +243,7 @@ remoting.CastExtensionHandler.prototype.chromotingMessageListener =
     function(ns, message) {
   if (ns === this.kCastNamespace_) {
     try {
-        var messageObj = getJsonObjectFromString(message);
+        var messageObj = base.getJsonObjectFromString(message);
         this.sendMessageToHost_(messageObj);
     } catch (err) {
       console.error('Failed to process message from Cast device.');