sheriff_o_matic: Add error if ajax request fails.

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

Index: appengine/sheriff_o_matic/model/ct-failure-group.html
diff --git a/appengine/sheriff_o_matic/model/ct-failure-group.html b/appengine/sheriff_o_matic/model/ct-failure-group.html
index 5d16c80a96b7bc96eed021a5a3d821992b9cd319..92508511ca3af5fb0f8335c50968ea4778ca1637 100644
--- a/appengine/sheriff_o_matic/model/ct-failure-group.html
+++ b/appengine/sheriff_o_matic/model/ct-failure-group.html
@@ -135,6 +135,10 @@ CTFailureGroup.prototype._updateAnnotation = function(kind, change) {
     var parsed = JSON.parse(data);
     CTFailureGroup._annotations[parsed.key] = parsed;
     this._computeProperties();
+  }.bind(this), function(reject) {
+    if (this.errorCallback) {
+      this.errorCallback(reject);
+    }
   }.bind(this));
 };