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

grpc/prpc/client.go

Index: grpc/prpc/client.go
diff --git a/grpc/prpc/client.go b/grpc/prpc/client.go
index ff6b68bbad95d5465b463491d7841d5c18779d5b..da61581ef6ed6be77fd0bbd76d07e51be1f5d58a 100644
--- a/grpc/prpc/client.go
+++ b/grpc/prpc/client.go
@@ -203,7 +203,8 @@ func (c *Client) CallRaw(ctx context.Context, serviceName, methodName string, in
 			}
 			if err != nil {
 				// Treat all errors here as transient.
-				return errors.WrapTransient(fmt.Errorf("failed to send request: %s", err))
+				return errors.Annotate(err).Reason("failed to send request").
+					Tag(retry.Tag).Err()
 			}
 
 			if options.resHeaderMetadata != nil {
@@ -266,7 +267,7 @@ func (c *Client) CallRaw(ctx context.Context, serviceName, methodName string, in
 				// AppEngine), and should be automatically retried even if a gRPC code
 				// header is not supplied.
 				if res.StatusCode >= http.StatusInternalServerError {
-					err = errors.WrapTransient(err)
+					err = retry.Tag.Apply(err)
 				}
 				return err
 			}
@@ -279,12 +280,7 @@ func (c *Client) CallRaw(ctx context.Context, serviceName, methodName string, in
 
 			code := codes.Code(codeInt)
 			if code != codes.OK {
-				desc := strings.TrimSuffix(buf.String(), "\n")
-				err := grpcutil.Errf(code, "%s", desc)
-				if grpcutil.IsTransientCode(code) {
-					err = errors.WrapTransient(err)
-				}
-				return err
+				return grpcutil.Errf(code, "%s", strings.TrimSuffix(buf.String(), "\n"))
 			}
 			return nil
 		},