Refactor distributor API so that methods always get the Quest_Desc too.

dm/appengine/distributor/notify_execution.go

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package distributor
 
 import (
+        "github.com/luci/gae/filter/txnBuf"
         "github.com/luci/gae/service/datastore"
+        "github.com/luci/luci-go/common/errors"
         "github.com/luci/luci-go/common/logging"
         "github.com/luci/luci-go/dm/appengine/model"
         "github.com/luci/luci-go/tumble"
         "golang.org/x/net/context"
 )
 
 // NotifyExecution is used to finish an execution. Specifically it allows the
 // appropriate distributor to HandleNotification, and then when that concludes,
 // invokes DM's FinishExecution (see mutate.FinishExecution).
 type NotifyExecution struct {
@@ skipping 10 matching lines @@
 func (f *NotifyExecution) RollForward(c context.Context) (muts []tumble.Mutation, err error) {
         reg := GetRegistry(c)
         dist, _, err := reg.MakeDistributor(c, f.CfgName)
         if err != nil {
                 logging.Fields{
                         logging.ErrorKey: err,
                         "cfg":            f.CfgName,
                 }.Errorf(c, "Failed to make distributor")
                 return
         }
-        rslt, err := dist.HandleNotification(f.Notification)
+        dsNoTx := txnBuf.GetNoTxn(c)
+        q := &model.Quest{ID: f.Notification.ID.Quest}
+        if err := dsNoTx.Get(q); err != nil {
+                return nil, errors.Annotate(err).Reason("getting Quest").Err()
+        }
+        rslt, err := dist.HandleNotification(&q.Desc, f.Notification)
         if err != nil {
                 // TODO(riannucci): check for transient/non-transient
                 logging.Fields{
                         logging.ErrorKey: err,
                         "cfg":            f.CfgName,
                 }.Errorf(c, "Failed to handle notification")
                 return
         }
         if rslt != nil {
                 return reg.FinishExecution(c, f.Notification.ID, rslt)
         }
         return
 }
 
 func init() {
         tumble.Register((*NotifyExecution)(nil))
 }