LogDog: Add Butler Output package.

client/internal/logdog/butler/output/retry.go

Index: client/internal/logdog/butler/output/retry.go
diff --git a/client/internal/logdog/butler/output/retry.go b/client/internal/logdog/butler/output/retry.go
new file mode 100644
index 0000000000000000000000000000000000000000..c85cb6d794c9730bab84a4503c3972e43b170e2a
--- /dev/null
+++ b/client/internal/logdog/butler/output/retry.go
@@ -0,0 +1,26 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package output
+
+import (
+	"time"
+
+	"github.com/luci/luci-go/common/retry"
+	"golang.org/x/net/context"
+)
+
+// DefaultRetryIterator returns a retry.Iterator configured with a default
+// exponential backoff retry configuration.
+func DefaultRetryIterator(context.Context) retry.Iterator {
+	// TODO: Tune backoff parameters.
+	return &retry.ExponentialBackoff{
+		Limited: retry.Limited{
+			Delay:    (500 * time.Millisecond),
+			Retries:  4,
+			MaxTotal: 20 * time.Second,
+		},
+		Multiplier: 2.0,
+	}
+}