Add dartdoc to the generated utils snapshot

sdk/lib/_internal/dartdoc/bin/dartdoc.dart

Index: sdk/lib/_internal/dartdoc/bin/dartdoc.dart
===================================================================
--- sdk/lib/_internal/dartdoc/bin/dartdoc.dart	(revision 21335)
+++ sdk/lib/_internal/dartdoc/bin/dartdoc.dart	(working copy)
@@ -29,11 +29,11 @@
 /**
  * Run this from the `lib/_internal/dartdoc` directory.
  */
-main() {
+mainWithOptions(Options options) {
   // Need this because ArgParser.getUsage doesn't show command invocation.
   final USAGE = 'Usage dartdoc [options] <entrypoint(s)>\n[options] include:';
 
-  final args = new Options().arguments;
+  final args = options.arguments;
 
   final dartdoc = new Dartdoc();
 
@@ -249,6 +249,10 @@
     .whenComplete(() => dartdoc.cleanup());
 }
 
+main() {
+  mainWithOptions(new Options());
+}
+
 String _getPackageRoot(List<Uri> entrypoints) {
   // Check if there's a `packages` directory in the entry point directory.
   var fileEntrypoint = entrypoints.firstWhere(