Add beginnings of new cr command

go/src/infra/tools/cr/main.go

Index: go/src/infra/tools/cr/main.go
diff --git a/go/src/infra/tools/cr/main.go b/go/src/infra/tools/cr/main.go
new file mode 100644
index 0000000000000000000000000000000000000000..ee876a46a8966671a8cf089c900c3f9b36b86108
--- /dev/null
+++ b/go/src/infra/tools/cr/main.go
@@ -0,0 +1,81 @@
+// 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.
+
+/*
+Core of the Chrome Infrastructure CLI SDK. Provides autoupdate, module
+discovery, module installation, and help.
+*/
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"infra/tools/cr/lib/subcommand"
+	"infra/tools/cr/lib/terminal"
+
+	_ "infra/tools/cr/cmd/firstrun"
+)
+
+var (
+	// The subcommand which will be executed.
+	cmd *subcommand.Subcommand
+
+	// Accessible variables for global flags.
+	help    bool
+	verbose bool
+)
+
+func printSubcommands() {
+	fmt.Println("Available subcommands are:")
+	subcommand.Tabulate()
+	fmt.Println("")
+}
+
+func printCrHelp() {
+	fmt.Print(`The cr tool intelligently manages the Chrome Infra command-line SDK.
+
+You must provide a subcommand. Run 'cr help' for a list of available commands.
+`)
+	printSubcommands()
+}
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Println("No subcommand provided.")
+		printCrHelp()
+		os.Exit(-1)
+	}
+
+	cmd := subcommand.Get(os.Args[1])
+	if cmd == nil {
+		fmt.Printf("Unrecognized subcommand '%v'.\n", os.Args[1])
+		printCrHelp()
+		os.Exit(-1)
+	}
+
+	flags := flag.NewFlagSet("flags", flag.ExitOnError)
+	flags.BoolVar(&help, "help", false, "print help for the given command")
+	flags.BoolVar(&verbose, "verbose", false, "print more verbose output")
+	cmd.InitFlags(flags)
+	flags.Parse(os.Args[2:])
+
+	if verbose {
+		terminal.ShowDebug = true
+	}
+
+	// There are two ways to get help: 'cr help foo' and 'cr foo --help'. The
+	// former is handled by setSubcommand, the latter is special-cased here.
+	if help {
+		cmd.Help(flags)
+		return
+	}
+
+	err := cmd.Run(flags)
+	if err != nil {
+		fmt.Print(err)
+	}
+}