Add beginnings of new cr command

go/src/infra/tools/cr/lib/subcommand/subcommand.go

Index: go/src/infra/tools/cr/lib/subcommand/subcommand.go
diff --git a/go/src/infra/tools/cr/lib/subcommand/subcommand.go b/go/src/infra/tools/cr/lib/subcommand/subcommand.go
new file mode 100644
index 0000000000000000000000000000000000000000..4604fb3ab09bb9263f3dd955f054ee6d686eb27d
--- /dev/null
+++ b/go/src/infra/tools/cr/lib/subcommand/subcommand.go
@@ -0,0 +1,46 @@
+// Copyright 2016 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.
+
+/*
+Library for defining subcommands in a structured way.
+*/
+
+package subcommand
+
+import (
+	"flag"
+	"fmt"
+)
+
+type Subcommand struct {
+	ShortHelp string
+	LongHelp  string
+	flagFn    func(*flag.FlagSet)
+	runFn     func(*flag.FlagSet) error
+}
+
+func New(shortHelp string, longHelp string, flagFn func(*flag.FlagSet), runFn func(*flag.FlagSet) error) *Subcommand {
+	return &Subcommand{shortHelp, longHelp, flagFn, runFn}
+}
+
+func (c *Subcommand) Help(flags *flag.FlagSet) {
+	fmt.Println(c.ShortHelp)
+	fmt.Println("")
+	fmt.Println(c.LongHelp)
+	fmt.Println("")
+	flags.PrintDefaults()
+}
+
+func (c *Subcommand) InitFlags(flags *flag.FlagSet) {
+	if c.flagFn != nil {
+		c.flagFn(flags)
+	}
+}
+
+func (c *Subcommand) Run(flags *flag.FlagSet) error {
+	if c.runFn != nil {
+		return c.runFn(flags)
+	}
+	return nil
+}