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

scheduler/appengine/task/swarming/swarming.go

Index: scheduler/appengine/task/swarming/swarming.go
diff --git a/scheduler/appengine/task/swarming/swarming.go b/scheduler/appengine/task/swarming/swarming.go
index 20928c55790c3645d5768e2d97994c94ad8302bb..8fbec30ecc01a9edbd03e454103f30ccb976ea6a 100644
--- a/scheduler/appengine/task/swarming/swarming.go
+++ b/scheduler/appengine/task/swarming/swarming.go
@@ -18,6 +18,7 @@ import (
 	"github.com/luci/gae/service/info"
 	"github.com/luci/luci-go/common/api/swarming/swarming/v1"
 	"github.com/luci/luci-go/common/errors"
+	"github.com/luci/luci-go/common/retry/transient"
 	"github.com/luci/luci-go/scheduler/appengine/messages"
 	"github.com/luci/luci-go/scheduler/appengine/task"
 	"github.com/luci/luci-go/scheduler/appengine/task/utils"
@@ -356,7 +357,7 @@ func (m TaskManager) checkTaskStatus(c context.Context, ctl task.Controller) err
 	// still running LaunchTask when saving the invocation, it will only make the
 	// matters worse.
 	case status == task.StatusStarting:
-		return errors.WrapTransient(errors.New("invocation is still starting, try again later"))
+		return errors.New("invocation is still starting, try again later", transient.Tag)
 	case status != task.StatusRunning:
 		return fmt.Errorf("unexpected invocation status %q, expecting %q", status, task.StatusRunning)
 	}
@@ -377,7 +378,7 @@ func (m TaskManager) checkTaskStatus(c context.Context, ctl task.Controller) err
 	if err != nil {
 		ctl.DebugLog("Failed to fetch task results - %s", err)
 		err = utils.WrapAPIError(err)
-		if !errors.IsTransient(err) {
+		if !transient.Tag.In(err) {
 			ctl.State().Status = task.StatusFailed
 		}
 		return err