LogDog: Add Butler Output package.

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

+// 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.

[estaab, 2015/11/19 23:57:24]

Should we allow any of these to be controlled by flags in case we need to change
something without needing to do a code push?

[dnj, 2015/11/20 01:55:12]

I originally had this. Then I read a ToTT on flag bloat saying, "if a flag isn't
being used, don't define it" and agreed with it.

Actually going to delete this altogether since the "retry" library defines this
now.

+        return &retry.ExponentialBackoff{
+                Limited: retry.Limited{
+                        Delay:    (500 * time.Millisecond),
+                        Retries:  4,
+                        MaxTotal: 20 * time.Second,
+                },
+                Multiplier: 2.0,
+        }
+}