Added isError method to remoting.Xhr.Error to check for HTTP errors.

remoting/webapp/crd/js/xhr.js

Index: remoting/webapp/crd/js/xhr.js
diff --git a/remoting/webapp/crd/js/xhr.js b/remoting/webapp/crd/js/xhr.js
index cc50b27745e4fce258f1715982795f436b6dd915..4b3603e7b5e913693f9642f53f5a95e8fee005f5 100644
--- a/remoting/webapp/crd/js/xhr.js
+++ b/remoting/webapp/crd/js/xhr.js
@@ -294,6 +294,14 @@ remoting.Xhr.Response = function(xhr, allowJson) {
 };
 
 /**
+ * @return {boolean} True if the response code is outside the 200-299
+ *     range (i.e. success as defined by the HTTP protocol).
+ */
+remoting.Xhr.Response.prototype.isError = function() {
+  return this.status < 200 || this.status >= 300;
+};
+
+/**
  * @return {string} The text content of the response.
  */
 remoting.Xhr.Response.prototype.getText = function() {