sheriff_o_matic: Add error if ajax request fails.

appengine/sheriff_o_matic/model/ct-failure-group.html

 <!--
 Copyright 2014 The Chromium Authors. All rights reserved.
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
 <link rel="import" href="ct-commit-list.html">
 <link rel="import" href="ct-tree-list.html">
 
 <script>
@@ skipping 117 matching lines @@
   fullChange[0][kind] = change;
 
   return net.ajax({
     type: 'POST',
     data: JSON.stringify(fullChange),
     url: '/api/v1/annotations/' + this.key,
   }).then(function(data) {
     var parsed = JSON.parse(data);
     CTFailureGroup._annotations[parsed.key] = parsed;
     this._computeProperties();
+  }.bind(this), function(reject) {
+    if (this.errorCallback) {
+      this.errorCallback(reject);
+    }
   }.bind(this));
 };
 
 
 CTFailureGroup.prototype.fetchAnnotations = function() {
   return net.json('/api/v1/annotations/' + this.key).then(function(data) {
     CTFailureGroup._annotations[data.key] = data;
     this._computeProperties();
   }.bind(this));
 };
 
 CTFailureGroup.fetchAllAnnotations = function() {
   return net.json('/api/v1/annotations').then(function(data) {
     if (CTFailureGroup._annotations == null) {
       CTFailureGroup._annotations = {};
     }
 
     data.forEach(function(annotation) {
       CTFailureGroup._annotations[annotation.key] = annotation;
     })
     return data;
   });
 };
 
 </script>