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

lib/src/formatter_options.dart

 // Copyright (c) 2014, 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.
 
 library dart_style.src.formatter_options;
 
 import 'dart:convert';
 import 'dart:io';
 
 import 'source_code.dart';
 
 /// Global options that affect how the formatter produces and uses its outputs.
 class FormatterOptions {
   /// The [OutputReporter] used to show the formatting results.
   final OutputReporter reporter;
 
+  /// The number of spaces of indentation to prefix the output with.
+  final int indent;
+
   /// The number of columns that formatted output should be constrained to fit
   /// within.
   final int pageWidth;
 
   /// Whether symlinks should be traversed when formatting a directory.
   final bool followLinks;
 
   FormatterOptions(this.reporter,
-      {this.pageWidth: 80, this.followLinks: false});
+      {this.indent: 0, this.pageWidth: 80, this.followLinks: false});
 }
 
 /// How the formatter reports the results it produces.
 abstract class OutputReporter {
   /// Prints only the names of files whose contents are different from their
   /// formatted version.
   static final dryRun = new _DryRunReporter();
 
   /// Prints the formatted results of each file to stdout.
   static final print = new _PrintReporter();
@@ skipping 151 matching lines @@
     var elapsed = new DateTime.now().difference(_ongoing.remove(label));
     if (elapsed.inMilliseconds >= 10) {
       _elapsed[label] = elapsed;
     } else {
       _elided++;
     }
 
     _inner.afterFile(file, label, output, changed: changed);
   }
 }