Add support for command-line editing to ddbg.

tools/ddbg/lib/terminfo.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert';
+import 'dart:io';
+
+int _tputGetInteger(String capName) {
+  var result = Process.runSync('tput',  ['$capName'], stdoutEncoding:UTF8);
+  if (result.exitCode != 0) {
+    return 0;
+  }
+  return int.parse(result.stdout);
+}
+
+String _tputGetSequence(String capName) {
+  var result = Process.runSync('tput',  ['$capName'], stdoutEncoding:UTF8);
+  if (result.exitCode != 0) {
+    return '';
+  }
+  return result.stdout;
+}
+
+class TermInfo {
+  TermInfo() {
+    resize();
+  }
+
+  int get lines => _lines;
+  int get cols => _cols;
+
+  int _lines;
+  int _cols;
+
+  void resize() {
+    _lines = _tputGetInteger('lines');
+    _cols = _tputGetInteger('cols');
+  }
+
+  // Back one character.
+  final String cursorBack = _tputGetSequence('cub1');
+
+  // Forward one character.
+  final String cursorForward = _tputGetSequence('cuf1');
+
+  // Up one character.
+  final String cursorUp = _tputGetSequence('cuu1');
+
+  // Down one character.
+  final String cursorDown = _tputGetSequence('cud1');
+
+  // Clear to end of line.
+  final String clrEOL = _tputGetSequence('el');
+
+  // Clear screen and home cursor.
+  final String clear = _tputGetSequence('clear');
+}