Add beginnings of new cr command

go/src/infra/tools/cr/lib/terminal/terminal.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.
+
+// Package terminal provides utilities for printing to and reading user input
+// from an interactive terminal.
+package terminal
+
+import (
+        "bufio"
+        "fmt"
+        "os"
+)
+
+// ShowDebug controls whether or not calls to terminal.Debug produce output.
+var ShowDebug = false
+
+// Print prints the given format string (and arguments) to standard out.
+func Print(format string, args ...interface{}) {
+        fmt.Println(fmt.Sprintf(format, args...))
+}
+
+// Debug is the same as Print, but only produces output if ShowDebug is true.
+func Debug(format string, args ...interface{}) {
+        if ShowDebug {
+                fmt.Println(fmt.Sprintf(format, args...))
+        }
+}
+
+// Prompt prints a string to standard out, then waits for a single line
+// of user input and returns it.
+func Prompt(prompt string) (string, error) {
+        fmt.Print(prompt)
+        reader := bufio.NewReader(os.Stdin)
+        return reader.ReadString('\n')
+}