Add "-i" to command line to specify leading indent.

bin/format.dart

 // Copyright (c) 2015, 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';
 
 import 'package:args/args.dart';
 
 import 'package:dart_style/src/dart_formatter.dart';
 import 'package:dart_style/src/formatter_exception.dart';
 import 'package:dart_style/src/formatter_options.dart';
 import 'package:dart_style/src/io.dart';
 import 'package:dart_style/src/source_code.dart';
 
 // Note: The following line of code is modified by tool/grind.dart.
 const version = "0.2.0+1";
 
 void main(List<String> args) {
   var parser = new ArgParser(allowTrailingOptions: true);
 
   parser.addFlag("help",
       abbr: "h", negatable: false, help: "Shows usage information.");
   parser.addFlag("version",
       negatable: false, help: "Shows version information.");
   parser.addOption("line-length",
       abbr: "l", help: "Wrap lines longer than this.", defaultsTo: "80");
+  parser.addOption("indent",
+      abbr: "i", help: "Spaces of leading indentation.", defaultsTo: "0");
   parser.addOption("preserve",
       help: 'Selection to preserve, formatted as "start:length".');
   parser.addFlag("dry-run",
       abbr: "n",
       negatable: false,
       help: "Show which files would be modified but make no changes.");
   parser.addFlag("overwrite",
       abbr: "w",
       negatable: false,
       help: "Overwrite input files with formatted output.");
@@ skipping 73 matching lines @@
     reporter = OutputReporter.overwrite;
   } else if (argResults["machine"]) {
     reporter = OutputReporter.printJson;
   }
 
   if (argResults["profile"]) {
     reporter = new ProfileReporter(reporter);
   }
 
   var pageWidth;
-
   try {
     pageWidth = int.parse(argResults["line-length"]);
   } on FormatException catch (_) {
     usageError(
         parser,
         '--line-length must be an integer, was '
         '"${argResults['line-length']}".');
   }
 
+  var indent;
+
+  try {
+    indent = int.parse(argResults["indent"]);
+    if (indent < 0 || indent.toInt() != indent) throw new FormatException();
+  } on FormatException catch (_) {
+    usageError(
+        parser,
+        '--indent must be a non-negative integer, was '
+        '"${argResults['indent']}".');
+  }
+
   var followLinks = argResults["follow-links"];
 
   var options = new FormatterOptions(reporter,
-      pageWidth: pageWidth, followLinks: followLinks);
+      indent: indent, pageWidth: pageWidth, followLinks: followLinks);
 
   if (argResults.rest.isEmpty) {
     formatStdin(options, selection);
   } else {
     formatPaths(options, argResults.rest);
   }
 
   if (argResults["profile"]) {
     (reporter as ProfileReporter).showProfile();
   }
@@ skipping 16 matching lines @@
   var selectionStart = 0;
   var selectionLength = 0;
 
   if (selection != null) {
     selectionStart = selection[0];
     selectionLength = selection[1];
   }
 
   var input = new StringBuffer();
   stdin.transform(new Utf8Decoder()).listen(input.write, onDone: () {
-    var formatter = new DartFormatter(pageWidth: options.pageWidth);
+    var formatter =
+        new DartFormatter(indent: options.indent, pageWidth: options.pageWidth);
     try {
       options.reporter.beforeFile(null, "<stdin>");
       var source = new SourceCode(input.toString(),
           uri: "stdin",
           selectionStart: selectionStart,
           selectionLength: selectionLength);
       var output = formatter.formatSource(source);
       options.reporter
           .afterFile(null, "<stdin>", output, changed: source != output);
       return true;
@@ skipping 47 matching lines @@
     output = stdout;
   }
 
   output.write("""$message
 
 Usage: dartfmt [-n|-w] [files or directories...]
 
 ${parser.usage}
 """);
 }