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

common/retry/transient.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 retry
-
-import (
-        "time"
-
-        "github.com/luci/luci-go/common/errors"
-        "golang.org/x/net/context"
-)
-
-// transientOnlyIterator is an Iterator implementation that only retries errors
-// if they are transient.
-//
-// (See errors.IsTransient).
-type transientOnlyIterator struct {
-        Iterator // The wrapped Iterator.
-}
-
-func (i *transientOnlyIterator) Next(ctx context.Context, err error) time.Duration {
-        if !errors.IsTransient(err) {
-                return Stop
-        }
-        return i.Iterator.Next(ctx, err)
-}
-
-// TransientOnly returns an Iterator that wraps another Iterator. It will fall
-// through to the wrapped Iterator if a transient error is encountered;
-// otherwise, it will not retry.
-// Returns nil if f is nil.
-func TransientOnly(f Factory) Factory {
-        if f == nil {
-                return nil
-        }
-        return wrap(f, func(it Iterator) Iterator {
-                return &transientOnlyIterator{it}
-        })
-}