[errors] Greatly simplify common/errors package.

logdog/client/cli/subcommandLatest.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 cli
 
 import (
         "io"
         "os"
 
@@ skipping 56 matching lines @@
                                 log.ErrorKey: err,
                                 "project":    addr.Project,
                                 "path":       addr.Path,
                         }.Errorf(a, "Invalid command-line stream path.")
                         return 1
                 }
         }
 
         coord, err := a.coordinatorClient(addr.Host)
         if err != nil {
-                errors.Log(a, errors.Annotate(err).Reason("failed to create Coordinator client").Err())
+                errors.Log(a, errors.Annotate(err, "failed to create Coordinator client").Err())
                 return 1
         }
 
         stream := coord.Stream(addr.Project, addr.Path)
 
         tctx, _ := a.timeoutCtx(a)
         le, st, err := cmd.getTailEntry(tctx, stream)
         if err != nil {
                 log.Fields{
                         log.ErrorKey: err,
@@ skipping 38 matching lines @@
                         if ar := <-clock.After(c, noStreamDelay); ar.Incomplete() {
                                 // Timer stopped prematurely.
                                 return nil, nil, ar.Err
                         }
 
                 default:
                         return nil, nil, err
                 }
         }
 }