Pass error messages from native messaging to web-app.

remoting/webapp/crd/js/host_daemon_facade.js

Index: remoting/webapp/crd/js/host_daemon_facade.js
diff --git a/remoting/webapp/crd/js/host_daemon_facade.js b/remoting/webapp/crd/js/host_daemon_facade.js
index 544abd39683d617c787e344caa5695f963b32a6a..62ae4ee2f79eb66d30c8345393acbe01c5213648 100644
--- a/remoting/webapp/crd/js/host_daemon_facade.js
+++ b/remoting/webapp/crd/js/host_daemon_facade.js
@@ -50,6 +50,10 @@ remoting.HostDaemonFacade = function() {
   /** @private */
   this.onDisconnectCallback_ = this.onDisconnect_.bind(this);
 
+  /** @private */
+  this.debugMessageHandler_ =
+      new remoting.NativeMessageHostDebugMessageHandler();
+
   this.initialize_();
 };
 
@@ -180,6 +184,10 @@ remoting.HostDaemonFacade.prototype.postMessageInternal_ = function(message) {
  * @private
  */
 remoting.HostDaemonFacade.prototype.onIncomingMessage_ = function(message) {
+  if (this.debugMessageHandler_.handleMessage(message)) {
+    return;
+  }
+
   /** @type {number} */
   var id = message['id'];
   if (typeof(id) != 'number') {