Change how to set the Dart name of a field

lib/src/dart_options.pb.dart

Index: lib/src/dart_options.pb.dart
diff --git a/lib/src/dart_options.pb.dart b/lib/src/dart_options.pb.dart
index a71c6e38b35c56bbd03178e5903cd3aff157df0c..ea4f48314695892d174f7d61c106f1a42b83ebcf 100644
--- a/lib/src/dart_options.pb.dart
+++ b/lib/src/dart_options.pb.dart
@@ -1,15 +1,18 @@
 ///
 //  Generated code. Do not modify.
 ///
-library dart_options;
+library dart_options_dart_options;
 
 import 'package:protobuf/protobuf.dart';
 
 class Dart_options {
-  static final Extension defaultMixin = new Extension('FileOptions', 'defaultMixin', 96128839, PbFieldType.OS);
-  static final Extension mixin = new Extension('MessageOptions', 'mixin', 96128839, PbFieldType.OS);
+  static final Extension defaultMixin = new Extension<String>('FileOptions', 'defaultMixin', 96128839, PbFieldType.OS);
+  static final Extension mixin = new Extension<String>('MessageOptions', 'mixin', 96128839, PbFieldType.OS);
+  static final Extension dartName = new Extension<String>('FieldOptions', 'dartName', 28700919, PbFieldType.OS);
   static void registerAllExtensions(ExtensionRegistry registry) {
     registry.add(defaultMixin);
     registry.add(mixin);
+    registry.add(dartName);
   }
 }
+