Add beginnings of new cr command

go/src/infra/tools/cr/cmd/firstrun/firstrun.go

Index: go/src/infra/tools/cr/cmd/firstrun/firstrun.go
diff --git a/go/src/infra/tools/cr/cmd/firstrun/firstrun.go b/go/src/infra/tools/cr/cmd/firstrun/firstrun.go
new file mode 100644
index 0000000000000000000000000000000000000000..a415d6d2a430b4a279cfd60d89160bd907aa674d
--- /dev/null
+++ b/go/src/infra/tools/cr/cmd/firstrun/firstrun.go
@@ -0,0 +1,62 @@
+// 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.
+
+// Package firstrun contains the logic for the 'cr firstrun' command.
+// Generally only executed once on a given machine, the firstrun command
+// installs the cr tool, prepares a space for it to install modules, and
+// adds it to $PATH.
+package firstrun
+
+import (
+	"flag"
+	"fmt"
+	"strings"
+
+	"infra/tools/cr/lib/subcommand"
+	"infra/tools/cr/lib/terminal"
+)
+
+var (
+	// Package-level variables for subcommand flags.
+	path string
+)
+
+var shortHelp = "Install the cr tool and intelligently add it to $PATH."
+
+var longHelp = `Given a path to a desired install directory, it takes ownership of that
+directory, sets it up to support installation of modules, and adds the
+directory to $PATH (by prompting to modify e.g. the registry or .bashrc).
+
+The firstrun command is intended to only be run once, when first
+installing the cr tool.
+
+Examples:
+  cr firstrun -verbose -path ~/local/bin/`
+
+func flags(flags *flag.FlagSet) {
+	flags.StringVar(&path, "path", "", "the path to install 'cr' in")
+}
+
+func run(flags *flag.FlagSet) error {
+	preinstall, err := firstrunCheckNotInstalled()
+	if err != nil {
+		terminal.Print("Had difficulty determining if cr is already installed. Continuing.")
+	}
+	if preinstall != "" {
+		prompt := fmt.Sprintf("It appears that cr is already installed at %v. Would you like to continue anyway? [y|N]", preinstall)
+		ans, err := terminal.Prompt(prompt)
+		if err != nil {
+			return fmt.Errorf("Failed to get user input.")
+		}
+		if !strings.HasPrefix(strings.ToLower(ans), "y") {
+			fmt.Printf("Aborting.")
+			return nil
+		}
+	}
+	// TODO(agable): Complement path flag with firstrunPromptInstallDir()
+	return firstrunInitInstallDir(path)
+}
+
+// FirstrunCmd is a subcommand.Command representing the 'cr firstrun' command.
+var FirstrunCmd = subcommand.New("firstrun", shortHelp, longHelp, flags, run)