[Dashboard] Formalize SeriesGroup

dashboard/dashboard/static/simple_xhr.html

Index: dashboard/dashboard/static/simple_xhr.html
diff --git a/dashboard/dashboard/static/simple_xhr.html b/dashboard/dashboard/static/simple_xhr.html
index 4e595f9bd02a7deea07a429966a37b58d0a93993..f9a353a5635d350cbe8da50d091d46bdc0e9f2c3 100644
--- a/dashboard/dashboard/static/simple_xhr.html
+++ b/dashboard/dashboard/static/simple_xhr.html
@@ -11,7 +11,7 @@ found in the LICENSE file.
 // This variable name is supposed to not be camelCased, in order for it
 // to match up with the file name.
 // eslint-disable-next-line
-var simple_xhr = (function() { 
+var simple_xhr = (function() {
 
   var LOGIN_ERROR_MESSAGE = 'Please check if you are logged in with a ' +
                             'google.com or chromium.org account in the ' +
@@ -66,9 +66,14 @@ var simple_xhr = (function() {
     return request;
   };
 
-  return {
-    send: send
+  var asPromise = function(url, params) {
+    return new Promise((resolve, reject) => {
+      simple_xhr.send(
+          url, params, response => resolve(response), error => reject(error));
+    });
   };
+
+  return {asPromise, send};
 })();
 
 </script>