Remove deprecated string features.

samples/chat/chat_server_lib.dart

Index: samples/chat/chat_server_lib.dart
diff --git a/samples/chat/chat_server_lib.dart b/samples/chat/chat_server_lib.dart
index cb3c02fbd651fc790a3bbc1f072bae4ae3db1d7f..ec195558662c0289ab5fd67c4319c8522a91f31e 100644
--- a/samples/chat/chat_server_lib.dart
+++ b/samples/chat/chat_server_lib.dart
@@ -311,7 +311,7 @@ class IsolatedServer {
                            HttpResponse response,
                            String redirectPath) {
     if (_redirectPage == null) {
-      _redirectPage = redirectPageHtml.charCodes;
+      _redirectPage = redirectPageHtml.codeUnits;
     }
     response.statusCode = HttpStatus.FOUND;
     response.headers.set(
@@ -355,7 +355,7 @@ class IsolatedServer {
   // Serve the not found page.
   void _notFoundHandler(HttpRequest request, HttpResponse response) {
     if (_notFoundPage == null) {
-      _notFoundPage = notFoundPageHtml.charCodes;
+      _notFoundPage = notFoundPageHtml.codeUnits;
     }
     response.statusCode = HttpStatus.NOT_FOUND;
     response.headers.set("Content-Type", "text/html; charset=UTF-8");