Use indentation for maps in lockfile.

sdk/lib/_internal/pub/lib/src/lock_file.dart

 // Copyright (c) 2012, 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 lock_file;
 
-import 'dart:json' as json;
 import 'dart:collection';
 
 import 'package:yaml/yaml.dart';
 
 import 'io.dart';
+import 'log.dart' as log;
 import 'package.dart';
 import 'source_registry.dart';
 import 'utils.dart';
 import 'version.dart';
 
 /// A parsed and validated `pubspec.lock` file.
 class LockFile {
   /// The packages this lockfile pins.
   Map<String, PackageId> packages;
 
@@ skipping 58 matching lines @@
 
         packages[name] = id;
       });
     }
 
     return new LockFile._(packages);
   }
 
   /// Returns the serialized YAML text of the lock file.
   String serialize() {
-    var packagesObj = new LinkedHashMap<String, Map>();
-
-    // Sort the packages by name.
-    var sortedKeys = packages.keys.toList();
-    sortedKeys.sort();
-    sortedKeys.forEach((name) {
-      packagesObj[name] = {
+    // Convert the dependencies to a simple object.
+    var data = {};
+    packages.forEach((name, package) {
+      data[name] = {
         'version': packages[name].version.toString(),
         'source': packages[name].source,
         'description': packages[name].description
       };
     });
 
-    // TODO(nweiz): Serialize using the YAML library once it supports
-    // serialization. For now, we use JSON, since it's a subset of YAML anyway.
-    return
-        '# Generated by pub\n'
-        '# See http://pub.dartlang.org/doc/glossary.html#lockfile\n'
-        '\n'
-        '${json.stringify({'packages': packagesObj})}\n';
+    return """
+# Generated by pub
+# See http://pub.dartlang.org/doc/glossary.html#lockfile
+${yamlToString({'packages': data})}
+""";
   }
 }