[alerts-dispatcher] update to build again :) also fixes a concurrent map access

go/src/infra/monitoring/messages/alerts.go

 // Copyright 2015 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.
 
 // Package alerts contains structs defined to implement the json format:
 // https://docs.google.com/document/d/10MESGzRy9uAy3Y3-PxUcjiuF3BD3FGGmCNvCjqm3WQQ/preview
 
 package messages
 
 import (
@@ skipping 96 matching lines @@
 type RegressionRange struct {
         Repo      string   `json:"repo"`
         URL       string   `json:"url"`
         Revisions []string `json:"revisions"`
         Positions []string `json:"positions"`
 }
 
 // RevisionSummary summarizes some information about a revision.
 type RevisionSummary struct {
         GitHash     string    `json:"git_hash"`
+        Position    string    `json:"commit_position"`
+        Branch      string    `json:"branch"`
         Link        string    `json:"link"`
         Description string    `json:"description"`
         Author      string    `json:"author"`
         When        EpochTime `json:"when"`
 }