Add beginnings of new cr command

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

+// 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)
+        }
+}