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

common/auth/internal/iam.go

 // Copyright 2017 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"
         "net/http"
 
         "golang.org/x/net/context"
         "golang.org/x/oauth2"
         "google.golang.org/api/googleapi"
 
-        "github.com/luci/luci-go/common/errors"
         "github.com/luci/luci-go/common/gcloud/googleoauth"
         "github.com/luci/luci-go/common/gcloud/iam"
+        "github.com/luci/luci-go/common/retry/transient"
 )
 
 type iamTokenProvider struct {
         actAs     string
         scopes    []string
         transport http.RoundTripper
         cacheKey  CacheKey
 }
 
 // NewIAMTokenProvider returns TokenProvider that uses SignBlob IAM API to
@@ skipping 35 matching lines @@
                         },
                 },
         })
         if err == nil {
                 return tok, nil
         }
         // Any 4** HTTP response is a fatal error. Everything else is transient.
         if apiErr, _ := err.(*googleapi.Error); apiErr != nil && apiErr.Code < 500 {
                 return nil, err
         }
-        return nil, errors.WrapTransient(err)
+        return nil, transient.Tag.Apply(err)
 }
 
 func (p *iamTokenProvider) RefreshToken(ctx context.Context, prev, base *oauth2.Token) (*oauth2.Token, error) {
         // Service account tokens are self sufficient, there's no need for refresh
         // token. Minting a token and "refreshing" it is a same thing.
         return p.MintToken(ctx, base)
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 
 type tokenInjectingTransport struct {
         transport http.RoundTripper
         token     *oauth2.Token
 }
 
 func (t *tokenInjectingTransport) RoundTrip(req *http.Request) (*http.Response, error) {
         clone := *req
         clone.Header = make(http.Header, len(req.Header)+1)
         for k, v := range req.Header {
                 clone.Header[k] = v
         }
         t.token.SetAuthHeader(&clone)
         return t.transport.RoundTrip(&clone)
 }