Add the ability to change the working directory

samples/build_dart/build.dart

Index: samples/build_dart/build.dart
diff --git a/samples/build_dart/build.dart b/samples/build_dart/build.dart
index 2f5ab68d4ade5633e1447d92808f76b4d359779a..215dc0a95b8aeda8171e2fdb51e71c18c5099485 100644
--- a/samples/build_dart/build.dart
+++ b/samples/build_dart/build.dart
@@ -72,7 +72,7 @@ void processArgs() {
  * Delete all generated files.
  */
 void handleCleanCommand() {
-  Directory current = new Directory.current();
+  Directory current = Directory.current;
   current.list(recursive: true).listen((FileSystemEntity entity) {
     if (entity is File) _maybeClean(entity);
   });
@@ -84,7 +84,7 @@ void handleCleanCommand() {
 void handleFullBuild() {
   var files = <String>[];
 
-  new Directory.current().list(recursive: true).listen(
+  Directory.current.list(recursive: true).listen(
       (FileSystemEntity entity) {
         if (entity is File) files.add(entity.fullPathSync());
       },