[errors] Greatly simplify common/errors package.

dm/appengine/mutate/add_deps.go

 // Copyright 2015 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 mutate
 
 import (
         ds "github.com/luci/gae/service/datastore"
         "github.com/luci/luci-go/common/data/bit_field"
         "github.com/luci/luci-go/common/errors"
@@ skipping 33 matching lines @@
         if err != nil {
                 return
         }
 
         if err = ResetExecutionTimeout(c, ex); err != nil {
                 logging.WithError(err).Errorf(c, "could not reset timeout")
                 return
         }
 
         fwdDeps, err := filterExisting(c, model.FwdDepsFromList(c, a.Auth.Id.AttemptID(), a.Deps))
-        err = errors.Annotate(err).Tag(grpcutil.Tag.With(codes.Internal)).
-                Reason("while filtering deps").Err()
+        err = errors.Annotate(err, "while filtering deps").Tag(grpcutil.Tag.With(codes.Internal)).Err()
         if err != nil || len(fwdDeps) == 0 {
                 return
         }
 
         logging.Fields{"aid": atmpt.ID, "count": len(fwdDeps)}.Infof(c, "added deps")
         atmpt.DepMap = bit_field.Make(uint32(len(fwdDeps)))
 
         for i, fdp := range fwdDeps {
                 fdp.BitIndex = uint32(i)
                 fdp.ForExecution = atmpt.CurExecution
         }
 
         if err = ds.Put(c, fwdDeps, atmpt, ex); err != nil {
-                err = errors.Annotate(err).Tag(grpcutil.Tag.With(codes.Internal)).
-                        Reason("putting stuff").Err()
+                err = errors.Annotate(err, "putting stuff").Tag(grpcutil.Tag.With(codes.Internal)).Err()
                 return
         }
 
         mergeQuestMap := map[string]*MergeQuest(nil)
         if len(a.Quests) > 0 {
                 mergeQuestMap = make(map[string]*MergeQuest, len(a.Quests))
                 for _, q := range a.Quests {
                         mergeQuestMap[q.ID] = &MergeQuest{Quest: q}
                 }
         }
@@ skipping 25 matching lines @@
         for _, mut := range mergeQuestMap {
                 muts = append(muts, mut)
         }
 
         return
 }
 
 func init() {
         tumble.Register((*AddDeps)(nil))
 }