[errors] de-specialize Transient in favor of Tags.

common/auth/internal/user.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 internal
 
 import (
         "fmt"
         "time"
 
         "golang.org/x/net/context"
         "golang.org/x/oauth2"
 
-        "github.com/luci/luci-go/common/errors"
         "github.com/luci/luci-go/common/logging"
+        "github.com/luci/luci-go/common/retry/transient"
 )
 
 type userAuthTokenProvider struct {
         config   *oauth2.Config
         cacheKey CacheKey
 }
 
 // NewUserAuthTokenProvider returns TokenProvider that can perform 3-legged
 // OAuth flow involving interaction with a user.
 func NewUserAuthTokenProvider(ctx context.Context, clientID, clientSecret string, scopes []string) (TokenProvider, error) {
@@ skipping 55 matching lines @@
 }
 
 func (p *userAuthTokenProvider) RefreshToken(ctx context.Context, prev, base *oauth2.Token) (*oauth2.Token, error) {
         // Clear expiration time to force token refresh. Do not use 0 since it means
         // that token never expires.
         t := *prev
         t.Expiry = time.Unix(1, 0)
         switch newTok, err := grabToken(p.config.TokenSource(ctx, &t)); {
         case err == nil:
                 return newTok, nil
-        case errors.IsTransient(err):
+        case transient.Tag.In(err):
                 logging.Warningf(ctx, "Transient error when refreshing the token - %s", err)
                 return nil, err
         default:
                 logging.Warningf(ctx, "Bad refresh token - %s", err)
                 return nil, ErrBadRefreshToken
         }
 }