Make String.charCodes a getter.

samples/markdown/markdown.dart

Index: samples/markdown/markdown.dart
diff --git a/samples/markdown/markdown.dart b/samples/markdown/markdown.dart
index 9bc1e53614b65882533889fc5a661dfa30f8e85f..c39da493f9fc8fb074d488e5484a43d90374ce2e 100644
--- a/samples/markdown/markdown.dart
+++ b/samples/markdown/markdown.dart
@@ -42,6 +42,6 @@ String readFile(String path) {
 void writeFile(String path, String text) {
   final file = new File(path);
   final stream = file.openOutputStream();
-  stream.write(text.charCodes());
+  stream.write(text.charCodes);
   stream.close();
 }