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

common/errors/transient.go

Index: common/errors/transient.go
diff --git a/common/errors/transient.go b/common/errors/transient.go
deleted file mode 100644
index 254e216edf2ffda9087a03a3f689a82583576d13..0000000000000000000000000000000000000000
--- a/common/errors/transient.go
+++ /dev/null
@@ -1,65 +0,0 @@
-// 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 errors
-
-// Transient is an Error implementation. It wraps an existing Error, marking
-// it as transient. This can be tested with IsTransient.
-type Transient interface {
-	error
-
-	// IsTransient returns true if this error type is transient.
-	IsTransient() bool
-}
-
-type transientWrapper struct {
-	error
-	finfo StackFrameInfo
-}
-
-var _ interface {
-	Transient
-	StackContexter
-} = transientWrapper{}
-
-func (t transientWrapper) IsTransient() bool {
-	return true
-}
-
-func (t transientWrapper) InnerError() error {
-	return t.error
-}
-
-func (t transientWrapper) StackContext() StackContext {
-	return StackContext{
-		FrameInfo:      t.finfo,
-		InternalReason: "errors.WrapTransient()",
-	}
-}
-
-// IsTransient tests if a given error or, if it is a container, any of its
-// contained errors is Transient.
-func IsTransient(err error) bool {
-	return Any(err, func(err error) bool {
-		if t, ok := err.(Transient); ok {
-			return t.IsTransient()
-		}
-		return false
-	})
-}
-
-// WrapTransient wraps an existing error with in a Transient error.
-//
-// If the supplied error is already Transient, it will be returned. If the
-// supplied error is nil, nil wil be returned.
-//
-// If the supplied error is not Transient, the current stack frame will be
-// captured. This wrapping action will show up on the stack trace returned by
-// RenderStack.
-func WrapTransient(err error) error {
-	if err == nil || IsTransient(err) {
-		return err
-	}
-	return transientWrapper{err, StackFrameInfoForError(1, err)}
-}